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diff --git a/Doc/whatsnew/3.3.rst b/Doc/whatsnew/3.3.rst new file mode 100644 index 0000000000..4ea49956f8 --- /dev/null +++ b/Doc/whatsnew/3.3.rst @@ -0,0 +1,2512 @@ +**************************** + What's New In Python 3.3 +**************************** + +.. Rules for maintenance: + + * Anyone can add text to this document. Do not spend very much time + on the wording of your changes, because your text will probably + get rewritten to some degree. + + * The maintainer will go through Misc/NEWS periodically and add + changes; it's therefore more important to add your changes to + Misc/NEWS than to this file. + + * This is not a complete list of every single change; completeness + is the purpose of Misc/NEWS. Some changes I consider too small + or esoteric to include. If such a change is added to the text, + I'll just remove it. (This is another reason you shouldn't spend + too much time on writing your addition.) + + * If you want to draw your new text to the attention of the + maintainer, add 'XXX' to the beginning of the paragraph or + section. + + * It's OK to just add a fragmentary note about a change. For + example: "XXX Describe the transmogrify() function added to the + socket module." The maintainer will research the change and + write the necessary text. + + * You can comment out your additions if you like, but it's not + necessary (especially when a final release is some months away). + + * Credit the author of a patch or bugfix. Just the name is + sufficient; the e-mail address isn't necessary. + + * It's helpful to add the bug/patch number as a comment: + + XXX Describe the transmogrify() function added to the socket + module. + (Contributed by P.Y. Developer in :issue:`12345`.) + + This saves the maintainer the effort of going through the Mercurial log + when researching a change. + +This article explains the new features in Python 3.3, compared to 3.2. +Python 3.3 was released on September 29, 2012. For full details, +see the `changelog <http://docs.python.org/3.3/whatsnew/changelog.html>`_. + +.. seealso:: + + :pep:`398` - Python 3.3 Release Schedule + + +Summary -- Release highlights +============================= + +.. This section singles out the most important changes in Python 3.3. + Brevity is key. + +New syntax features: + +* New ``yield from`` expression for :ref:`generator delegation <pep-380>`. +* The ``u'unicode'`` syntax is accepted again for :class:`str` objects. + +New library modules: + +* :mod:`faulthandler` (helps debugging low-level crashes) +* :mod:`ipaddress` (high-level objects representing IP addresses and masks) +* :mod:`lzma` (compress data using the XZ / LZMA algorithm) +* :mod:`unittest.mock` (replace parts of your system under test with mock objects) +* :mod:`venv` (Python :ref:`virtual environments <pep-405>`, as in the + popular ``virtualenv`` package) + +New built-in features: + +* Reworked :ref:`I/O exception hierarchy <pep-3151>`. + +Implementation improvements: + +* Rewritten :ref:`import machinery <importlib>` based on :mod:`importlib`. +* More compact :ref:`unicode strings <pep-393>`. +* More compact :ref:`attribute dictionaries <pep-412>`. + +Significantly Improved Library Modules: + +* C Accelerator for the :ref:`decimal <new-decimal>` module. +* Better unicode handling in the :ref:`email <new-email>` module + (:term:`provisional <provisional package>`). + +Security improvements: + +* Hash randomization is switched on by default. + +Please read on for a comprehensive list of user-facing changes. + + +.. _pep-405: + +PEP 405: Virtual Environments +============================= + +Virtual environments help create separate Python setups while sharing a +system-wide base install, for ease of maintenance. Virtual environments +have their own set of private site packages (i.e. locally-installed +libraries), and are optionally segregated from the system-wide site +packages. Their concept and implementation are inspired by the popular +``virtualenv`` third-party package, but benefit from tighter integration +with the interpreter core. + +This PEP adds the :mod:`venv` module for programmatic access, and the +:ref:`pyvenv <scripts-pyvenv>` script for command-line access and +administration. The Python interpreter checks for a ``pyvenv.cfg``, +file whose existence signals the base of a virtual environment's directory +tree. + +.. seealso:: + + :pep:`405` - Python Virtual Environments + PEP written by Carl Meyer; implementation by Carl Meyer and Vinay Sajip + + +PEP 420: Implicit Namespace Packages +==================================== + +Native support for package directories that don't require ``__init__.py`` +marker files and can automatically span multiple path segments (inspired by +various third party approaches to namespace packages, as described in +:pep:`420`) + +.. seealso:: + + :pep:`420` - Implicit Namespace Packages + PEP written by Eric V. Smith; implementation by Eric V. Smith + and Barry Warsaw + + +.. _pep-3118-update: + +PEP 3118: New memoryview implementation and buffer protocol documentation +========================================================================= + +The implementation of :pep:`3118` has been significantly improved. + +The new memoryview implementation comprehensively fixes all ownership and +lifetime issues of dynamically allocated fields in the Py_buffer struct +that led to multiple crash reports. Additionally, several functions that +crashed or returned incorrect results for non-contiguous or multi-dimensional +input have been fixed. + +The memoryview object now has a PEP-3118 compliant getbufferproc() +that checks the consumer's request type. Many new features have been +added, most of them work in full generality for non-contiguous arrays +and arrays with suboffsets. + +The documentation has been updated, clearly spelling out responsibilities +for both exporters and consumers. Buffer request flags are grouped into +basic and compound flags. The memory layout of non-contiguous and +multi-dimensional NumPy-style arrays is explained. + +Features +-------- + +* All native single character format specifiers in struct module syntax + (optionally prefixed with '@') are now supported. + +* With some restrictions, the cast() method allows changing of format and + shape of C-contiguous arrays. + +* Multi-dimensional list representations are supported for any array type. + +* Multi-dimensional comparisons are supported for any array type. + +* One-dimensional memoryviews of hashable (read-only) types with formats B, + b or c are now hashable. (Contributed by Antoine Pitrou in :issue:`13411`) + +* Arbitrary slicing of any 1-D arrays type is supported. For example, it + is now possible to reverse a memoryview in O(1) by using a negative step. + +API changes +----------- + +* The maximum number of dimensions is officially limited to 64. + +* The representation of empty shape, strides and suboffsets is now + an empty tuple instead of None. + +* Accessing a memoryview element with format 'B' (unsigned bytes) + now returns an integer (in accordance with the struct module syntax). + For returning a bytes object the view must be cast to 'c' first. + +* memoryview comparisons now use the logical structure of the operands + and compare all array elements by value. All format strings in struct + module syntax are supported. Views with unrecognised format strings + are still permitted, but will always compare as unequal, regardless + of view contents. + +* For further changes see `Build and C API Changes`_ and `Porting C code`_ . + +(Contributed by Stefan Krah in :issue:`10181`) + +.. seealso:: + + :pep:`3118` - Revising the Buffer Protocol + + +.. _pep-393: + +PEP 393: Flexible String Representation +======================================= + +The Unicode string type is changed to support multiple internal +representations, depending on the character with the largest Unicode ordinal +(1, 2, or 4 bytes) in the represented string. This allows a space-efficient +representation in common cases, but gives access to full UCS-4 on all +systems. For compatibility with existing APIs, several representations may +exist in parallel; over time, this compatibility should be phased out. + +On the Python side, there should be no downside to this change. + +On the C API side, PEP 393 is fully backward compatible. The legacy API +should remain available at least five years. Applications using the legacy +API will not fully benefit of the memory reduction, or - worse - may use +a bit more memory, because Python may have to maintain two versions of each +string (in the legacy format and in the new efficient storage). + +Functionality +------------- + +Changes introduced by :pep:`393` are the following: + +* Python now always supports the full range of Unicode codepoints, including + non-BMP ones (i.e. from ``U+0000`` to ``U+10FFFF``). The distinction between + narrow and wide builds no longer exists and Python now behaves like a wide + build, even under Windows. + +* With the death of narrow builds, the problems specific to narrow builds have + also been fixed, for example: + + * :func:`len` now always returns 1 for non-BMP characters, + so ``len('\U0010FFFF') == 1``; + + * surrogate pairs are not recombined in string literals, + so ``'\uDBFF\uDFFF' != '\U0010FFFF'``; + + * indexing or slicing non-BMP characters returns the expected value, + so ``'\U0010FFFF'[0]`` now returns ``'\U0010FFFF'`` and not ``'\uDBFF'``; + + * all other functions in the standard library now correctly handle + non-BMP codepoints. + +* The value of :data:`sys.maxunicode` is now always ``1114111`` (``0x10FFFF`` + in hexadecimal). The :c:func:`PyUnicode_GetMax` function still returns + either ``0xFFFF`` or ``0x10FFFF`` for backward compatibility, and it should + not be used with the new Unicode API (see :issue:`13054`). + +* The :file:`./configure` flag ``--with-wide-unicode`` has been removed. + +Performance and resource usage +------------------------------ + +The storage of Unicode strings now depends on the highest codepoint in the string: + +* pure ASCII and Latin1 strings (``U+0000-U+00FF``) use 1 byte per codepoint; + +* BMP strings (``U+0000-U+FFFF``) use 2 bytes per codepoint; + +* non-BMP strings (``U+10000-U+10FFFF``) use 4 bytes per codepoint. + +The net effect is that for most applications, memory usage of string +storage should decrease significantly - especially compared to former +wide unicode builds - as, in many cases, strings will be pure ASCII +even in international contexts (because many strings store non-human +language data, such as XML fragments, HTTP headers, JSON-encoded data, +etc.). We also hope that it will, for the same reasons, increase CPU +cache efficiency on non-trivial applications. The memory usage of +Python 3.3 is two to three times smaller than Python 3.2, and a little +bit better than Python 2.7, on a Django benchmark (see the PEP for +details). + +.. seealso:: + + :pep:`393` - Flexible String Representation + PEP written by Martin von Löwis; implementation by Torsten Becker + and Martin von Löwis. + + +.. _pep-397: + +PEP 397: Python Launcher for Windows +==================================== + +The Python 3.3 Windows installer now includes a ``py`` launcher application +that can be used to launch Python applications in a version independent +fashion. + +This launcher is invoked implicitly when double-clicking ``*.py`` files. +If only a single Python version is installed on the system, that version +will be used to run the file. If multiple versions are installed, the most +recent version is used by default, but this can be overridden by including +a Unix-style "shebang line" in the Python script. + +The launcher can also be used explicitly from the command line as the ``py`` +application. Running ``py`` follows the same version selection rules as +implicitly launching scripts, but a more specific version can be selected +by passing appropriate arguments (such as ``-3`` to request Python 3 when +Python 2 is also installed, or ``-2.6`` to specifclly request an earlier +Python version when a more recent version is installed). + +In addition to the launcher, the Windows installer now includes an +option to add the newly installed Python to the system PATH (contributed +by Brian Curtin in :issue:`3561`). + +.. seealso:: + + :pep:`397` - Python Launcher for Windows + PEP written by Mark Hammond and Martin v. Löwis; implementation by + Vinay Sajip. + + Launcher documentation: :ref:`launcher` + + Installer PATH modification: :ref:`windows-path-mod` + + +.. _pep-3151: + +PEP 3151: Reworking the OS and IO exception hierarchy +===================================================== + +The hierarchy of exceptions raised by operating system errors is now both +simplified and finer-grained. + +You don't have to worry anymore about choosing the appropriate exception +type between :exc:`OSError`, :exc:`IOError`, :exc:`EnvironmentError`, +:exc:`WindowsError`, :exc:`mmap.error`, :exc:`socket.error` or +:exc:`select.error`. All these exception types are now only one: +:exc:`OSError`. The other names are kept as aliases for compatibility +reasons. + +Also, it is now easier to catch a specific error condition. Instead of +inspecting the ``errno`` attribute (or ``args[0]``) for a particular +constant from the :mod:`errno` module, you can catch the adequate +:exc:`OSError` subclass. The available subclasses are the following: + +* :exc:`BlockingIOError` +* :exc:`ChildProcessError` +* :exc:`ConnectionError` +* :exc:`FileExistsError` +* :exc:`FileNotFoundError` +* :exc:`InterruptedError` +* :exc:`IsADirectoryError` +* :exc:`NotADirectoryError` +* :exc:`PermissionError` +* :exc:`ProcessLookupError` +* :exc:`TimeoutError` + +And the :exc:`ConnectionError` itself has finer-grained subclasses: + +* :exc:`BrokenPipeError` +* :exc:`ConnectionAbortedError` +* :exc:`ConnectionRefusedError` +* :exc:`ConnectionResetError` + +Thanks to the new exceptions, common usages of the :mod:`errno` can now be +avoided. For example, the following code written for Python 3.2:: + + from errno import ENOENT, EACCES, EPERM + + try: + with open("document.txt") as f: + content = f.read() + except IOError as err: + if err.errno == ENOENT: + print("document.txt file is missing") + elif err.errno in (EACCES, EPERM): + print("You are not allowed to read document.txt") + else: + raise + +can now be written without the :mod:`errno` import and without manual +inspection of exception attributes:: + + try: + with open("document.txt") as f: + content = f.read() + except FileNotFoundError: + print("document.txt file is missing") + except PermissionError: + print("You are not allowed to read document.txt") + +.. seealso:: + + :pep:`3151` - Reworking the OS and IO Exception Hierarchy + PEP written and implemented by Antoine Pitrou + + +.. index:: + single: yield; yield from (in What's New) + +.. _pep-380: + +PEP 380: Syntax for Delegating to a Subgenerator +================================================ + +PEP 380 adds the ``yield from`` expression, allowing a :term:`generator` to +delegate +part of its operations to another generator. This allows a section of code +containing :keyword:`yield` to be factored out and placed in another generator. +Additionally, the subgenerator is allowed to return with a value, and the +value is made available to the delegating generator. + +While designed primarily for use in delegating to a subgenerator, the ``yield +from`` expression actually allows delegation to arbitrary subiterators. + +For simple iterators, ``yield from iterable`` is essentially just a shortened +form of ``for item in iterable: yield item``:: + + >>> def g(x): + ... yield from range(x, 0, -1) + ... yield from range(x) + ... + >>> list(g(5)) + [5, 4, 3, 2, 1, 0, 1, 2, 3, 4] + +However, unlike an ordinary loop, ``yield from`` allows subgenerators to +receive sent and thrown values directly from the calling scope, and +return a final value to the outer generator:: + + >>> def accumulate(): + ... tally = 0 + ... while 1: + ... next = yield + ... if next is None: + ... return tally + ... tally += next + ... + >>> def gather_tallies(tallies): + ... while 1: + ... tally = yield from accumulate() + ... tallies.append(tally) + ... + >>> tallies = [] + >>> acc = gather_tallies(tallies) + >>> next(acc) # Ensure the accumulator is ready to accept values + >>> for i in range(4): + ... acc.send(i) + ... + >>> acc.send(None) # Finish the first tally + >>> for i in range(5): + ... acc.send(i) + ... + >>> acc.send(None) # Finish the second tally + >>> tallies + [6, 10] + +The main principle driving this change is to allow even generators that are +designed to be used with the ``send`` and ``throw`` methods to be split into +multiple subgenerators as easily as a single large function can be split into +multiple subfunctions. + +.. seealso:: + + :pep:`380` - Syntax for Delegating to a Subgenerator + PEP written by Greg Ewing; implementation by Greg Ewing, integrated into + 3.3 by Renaud Blanch, Ryan Kelly and Nick Coghlan; documentation by + Zbigniew Jędrzejewski-Szmek and Nick Coghlan + + +PEP 409: Suppressing exception context +====================================== + +PEP 409 introduces new syntax that allows the display of the chained +exception context to be disabled. This allows cleaner error messages in +applications that convert between exception types:: + + >>> class D: + ... def __init__(self, extra): + ... self._extra_attributes = extra + ... def __getattr__(self, attr): + ... try: + ... return self._extra_attributes[attr] + ... except KeyError: + ... raise AttributeError(attr) from None + ... + >>> D({}).x + Traceback (most recent call last): + File "<stdin>", line 1, in <module> + File "<stdin>", line 8, in __getattr__ + AttributeError: x + +Without the ``from None`` suffix to suppress the cause, the original +exception would be displayed by default:: + + >>> class C: + ... def __init__(self, extra): + ... self._extra_attributes = extra + ... def __getattr__(self, attr): + ... try: + ... return self._extra_attributes[attr] + ... except KeyError: + ... raise AttributeError(attr) + ... + >>> C({}).x + Traceback (most recent call last): + File "<stdin>", line 6, in __getattr__ + KeyError: 'x' + + During handling of the above exception, another exception occurred: + + Traceback (most recent call last): + File "<stdin>", line 1, in <module> + File "<stdin>", line 8, in __getattr__ + AttributeError: x + +No debugging capability is lost, as the original exception context remains +available if needed (for example, if an intervening library has incorrectly +suppressed valuable underlying details):: + + >>> try: + ... D({}).x + ... except AttributeError as exc: + ... print(repr(exc.__context__)) + ... + KeyError('x',) + +.. seealso:: + + :pep:`409` - Suppressing exception context + PEP written by Ethan Furman; implemented by Ethan Furman and Nick + Coghlan. + + +PEP 414: Explicit Unicode literals +====================================== + +To ease the transition from Python 2 for Unicode aware Python applications +that make heavy use of Unicode literals, Python 3.3 once again supports the +"``u``" prefix for string literals. This prefix has no semantic significance +in Python 3, it is provided solely to reduce the number of purely mechanical +changes in migrating to Python 3, making it easier for developers to focus on +the more significant semantic changes (such as the stricter default +separation of binary and text data). + +.. seealso:: + + :pep:`414` - Explicit Unicode literals + PEP written by Armin Ronacher. + + +PEP 3155: Qualified name for classes and functions +================================================== + +Functions and class objects have a new ``__qualname__`` attribute representing +the "path" from the module top-level to their definition. For global functions +and classes, this is the same as ``__name__``. For other functions and classes, +it provides better information about where they were actually defined, and +how they might be accessible from the global scope. + +Example with (non-bound) methods:: + + >>> class C: + ... def meth(self): + ... pass + >>> C.meth.__name__ + 'meth' + >>> C.meth.__qualname__ + 'C.meth' + +Example with nested classes:: + + >>> class C: + ... class D: + ... def meth(self): + ... pass + ... + >>> C.D.__name__ + 'D' + >>> C.D.__qualname__ + 'C.D' + >>> C.D.meth.__name__ + 'meth' + >>> C.D.meth.__qualname__ + 'C.D.meth' + +Example with nested functions:: + + >>> def outer(): + ... def inner(): + ... pass + ... return inner + ... + >>> outer().__name__ + 'inner' + >>> outer().__qualname__ + 'outer.<locals>.inner' + +The string representation of those objects is also changed to include the +new, more precise information:: + + >>> str(C.D) + "<class '__main__.C.D'>" + >>> str(C.D.meth) + '<function C.D.meth at 0x7f46b9fe31e0>' + +.. seealso:: + + :pep:`3155` - Qualified name for classes and functions + PEP written and implemented by Antoine Pitrou. + + +.. _pep-412: + +PEP 412: Key-Sharing Dictionary +=============================== + +Dictionaries used for the storage of objects' attributes are now able to +share part of their internal storage between each other (namely, the part +which stores the keys and their respective hashes). This reduces the memory +consumption of programs creating many instances of non-builtin types. + +.. seealso:: + + :pep:`412` - Key-Sharing Dictionary + PEP written and implemented by Mark Shannon. + + +PEP 362: Function Signature Object +================================== + +A new function :func:`inspect.signature` makes introspection of python +callables easy and straightforward. A broad range of callables is supported: +python functions, decorated or not, classes, and :func:`functools.partial` +objects. New classes :class:`inspect.Signature`, :class:`inspect.Parameter` +and :class:`inspect.BoundArguments` hold information about the call signatures, +such as, annotations, default values, parameters kinds, and bound arguments, +which considerably simplifies writing decorators and any code that validates +or amends calling signatures or arguments. + +.. seealso:: + + :pep:`362`: - Function Signature Object + PEP written by Brett Cannon, Yury Selivanov, Larry Hastings, Jiwon Seo; + implemented by Yury Selivanov. + + +PEP 421: Adding sys.implementation +================================== + +A new attribute on the :mod:`sys` module exposes details specific to the +implementation of the currently running interpreter. The initial set of +attributes on :attr:`sys.implementation` are ``name``, ``version``, +``hexversion``, and ``cache_tag``. + +The intention of ``sys.implementation`` is to consolidate into one namespace +the implementation-specific data used by the standard library. This allows +different Python implementations to share a single standard library code base +much more easily. In its initial state, ``sys.implementation`` holds only a +small portion of the implementation-specific data. Over time that ratio will +shift in order to make the standard library more portable. + +One example of improved standard library portability is ``cache_tag``. As of +Python 3.3, ``sys.implementation.cache_tag`` is used by :mod:`importlib` to +support :pep:`3147` compliance. Any Python implementation that uses +``importlib`` for its built-in import system may use ``cache_tag`` to control +the caching behavior for modules. + +SimpleNamespace +--------------- + +The implementation of ``sys.implementation`` also introduces a new type to +Python: :class:`types.SimpleNamespace`. In contrast to a mapping-based +namespace, like :class:`dict`, ``SimpleNamespace`` is attribute-based, like +:class:`object`. However, unlike ``object``, ``SimpleNamespace`` instances +are writable. This means that you can add, remove, and modify the namespace +through normal attribute access. + +.. seealso:: + + :pep:`421` - Adding sys.implementation + PEP written and implemented by Eric Snow. + + +.. _importlib: + +Using importlib as the Implementation of Import +=============================================== +:issue:`2377` - Replace __import__ w/ importlib.__import__ +:issue:`13959` - Re-implement parts of :mod:`imp` in pure Python +:issue:`14605` - Make import machinery explicit +:issue:`14646` - Require loaders set __loader__ and __package__ + +The :func:`__import__` function is now powered by :func:`importlib.__import__`. +This work leads to the completion of "phase 2" of :pep:`302`. There are +multiple benefits to this change. First, it has allowed for more of the +machinery powering import to be exposed instead of being implicit and hidden +within the C code. It also provides a single implementation for all Python VMs +supporting Python 3.3 to use, helping to end any VM-specific deviations in +import semantics. And finally it eases the maintenance of import, allowing for +future growth to occur. + +For the common user, there should be no visible change in semantics. For +those whose code currently manipulates import or calls import +programmatically, the code changes that might possibly be required are covered +in the `Porting Python code`_ section of this document. + +New APIs +-------- +One of the large benefits of this work is the exposure of what goes into +making the import statement work. That means the various importers that were +once implicit are now fully exposed as part of the :mod:`importlib` package. + +The abstract base classes defined in :mod:`importlib.abc` have been expanded +to properly delineate between :term:`meta path finders <meta path finder>` +and :term:`path entry finders <path entry finder>` by introducing +:class:`importlib.abc.MetaPathFinder` and +:class:`importlib.abc.PathEntryFinder`, respectively. The old ABC of +:class:`importlib.abc.Finder` is now only provided for backwards-compatibility +and does not enforce any method requirements. + +In terms of finders, :class:`importlib.machinery.FileFinder` exposes the +mechanism used to search for source and bytecode files of a module. Previously +this class was an implicit member of :attr:`sys.path_hooks`. + +For loaders, the new abstract base class :class:`importlib.abc.FileLoader` helps +write a loader that uses the file system as the storage mechanism for a module's +code. The loader for source files +(:class:`importlib.machinery.SourceFileLoader`), sourceless bytecode files +(:class:`importlib.machinery.SourcelessFileLoader`), and extension modules +(:class:`importlib.machinery.ExtensionFileLoader`) are now available for +direct use. + +:exc:`ImportError` now has ``name`` and ``path`` attributes which are set when +there is relevant data to provide. The message for failed imports will also +provide the full name of the module now instead of just the tail end of the +module's name. + +The :func:`importlib.invalidate_caches` function will now call the method with +the same name on all finders cached in :attr:`sys.path_importer_cache` to help +clean up any stored state as necessary. + +Visible Changes +--------------- + +For potential required changes to code, see the `Porting Python code`_ +section. + +Beyond the expanse of what :mod:`importlib` now exposes, there are other +visible changes to import. The biggest is that :attr:`sys.meta_path` and +:attr:`sys.path_hooks` now store all of the meta path finders and path entry +hooks used by import. Previously the finders were implicit and hidden within +the C code of import instead of being directly exposed. This means that one can +now easily remove or change the order of the various finders to fit one's needs. + +Another change is that all modules have a ``__loader__`` attribute, storing the +loader used to create the module. :pep:`302` has been updated to make this +attribute mandatory for loaders to implement, so in the future once 3rd-party +loaders have been updated people will be able to rely on the existence of the +attribute. Until such time, though, import is setting the module post-load. + +Loaders are also now expected to set the ``__package__`` attribute from +:pep:`366`. Once again, import itself is already setting this on all loaders +from :mod:`importlib` and import itself is setting the attribute post-load. + +``None`` is now inserted into :attr:`sys.path_importer_cache` when no finder +can be found on :attr:`sys.path_hooks`. Since :class:`imp.NullImporter` is not +directly exposed on :attr:`sys.path_hooks` it could no longer be relied upon to +always be available to use as a value representing no finder found. + +All other changes relate to semantic changes which should be taken into +consideration when updating code for Python 3.3, and thus should be read about +in the `Porting Python code`_ section of this document. + +(Implementation by Brett Cannon) + + +Other Language Changes +====================== + +Some smaller changes made to the core Python language are: + +* Added support for Unicode name aliases and named sequences. + Both :func:`unicodedata.lookup()` and ``'\N{...}'`` now resolve name aliases, + and :func:`unicodedata.lookup()` resolves named sequences too. + + (Contributed by Ezio Melotti in :issue:`12753`) + +* Unicode database updated to UCD version 6.1.0 + +* Equality comparisons on :func:`range` objects now return a result reflecting + the equality of the underlying sequences generated by those range objects. + (:issue:`13201`) + +* The ``count()``, ``find()``, ``rfind()``, ``index()`` and ``rindex()`` + methods of :class:`bytes` and :class:`bytearray` objects now accept an + integer between 0 and 255 as their first argument. + + (Contributed by Petri Lehtinen in :issue:`12170`) + +* The ``rjust()``, ``ljust()``, and ``center()`` methods of :class:`bytes` + and :class:`bytearray` now accept a :class:`bytearray` for the ``fill`` + argument. (Contributed by Petri Lehtinen in :issue:`12380`.) + +* New methods have been added to :class:`list` and :class:`bytearray`: + ``copy()`` and ``clear()`` (:issue:`10516`). Consequently, + :class:`~collections.abc.MutableSequence` now also defines a + :meth:`~collections.abc.MutableSequence.clear` method (:issue:`11388`). + +* Raw bytes literals can now be written ``rb"..."`` as well as ``br"..."``. + + (Contributed by Antoine Pitrou in :issue:`13748`.) + +* :meth:`dict.setdefault` now does only one lookup for the given key, making + it atomic when used with built-in types. + + (Contributed by Filip Gruszczyński in :issue:`13521`.) + +* The error messages produced when a function call does not match the function + signature have been significantly improved. + + (Contributed by Benjamin Peterson.) + + +A Finer-Grained Import Lock +=========================== + +Previous versions of CPython have always relied on a global import lock. +This led to unexpected annoyances, such as deadlocks when importing a module +would trigger code execution in a different thread as a side-effect. +Clumsy workarounds were sometimes employed, such as the +:c:func:`PyImport_ImportModuleNoBlock` C API function. + +In Python 3.3, importing a module takes a per-module lock. This correctly +serializes importation of a given module from multiple threads (preventing +the exposure of incompletely initialized modules), while eliminating the +aforementioned annoyances. + +(Contributed by Antoine Pitrou in :issue:`9260`.) + + +Builtin functions and types +=========================== + +* :func:`open` gets a new *opener* parameter: the underlying file descriptor + for the file object is then obtained by calling *opener* with (*file*, + *flags*). It can be used to use custom flags like :data:`os.O_CLOEXEC` for + example. The ``'x'`` mode was added: open for exclusive creation, failing if + the file already exists. +* :func:`print`: added the *flush* keyword argument. If the *flush* keyword + argument is true, the stream is forcibly flushed. +* :func:`hash`: hash randomization is enabled by default, see + :meth:`object.__hash__` and :envvar:`PYTHONHASHSEED`. +* The :class:`str` type gets a new :meth:`~str.casefold` method: return a + casefolded copy of the string, casefolded strings may be used for caseless + matching. For example, ``'ß'.casefold()`` returns ``'ss'``. +* The sequence documentation has been substantially rewritten to better + explain the binary/text sequence distinction and to provide specific + documentation sections for the individual builtin sequence types + (:issue:`4966`) + + +New Modules +=========== + +faulthandler +------------ + +This new debug module :mod:`faulthandler` contains functions to dump Python tracebacks explicitly, +on a fault (a crash like a segmentation fault), after a timeout, or on a user +signal. Call :func:`faulthandler.enable` to install fault handlers for the +:const:`SIGSEGV`, :const:`SIGFPE`, :const:`SIGABRT`, :const:`SIGBUS`, and +:const:`SIGILL` signals. You can also enable them at startup by setting the +:envvar:`PYTHONFAULTHANDLER` environment variable or by using :option:`-X` +``faulthandler`` command line option. + +Example of a segmentation fault on Linux: :: + + $ python -q -X faulthandler + >>> import ctypes + >>> ctypes.string_at(0) + Fatal Python error: Segmentation fault + + Current thread 0x00007fb899f39700: + File "/home/python/cpython/Lib/ctypes/__init__.py", line 486 in string_at + File "<stdin>", line 1 in <module> + Segmentation fault + + +ipaddress +--------- + +The new :mod:`ipaddress` module provides tools for creating and manipulating +objects representing IPv4 and IPv6 addresses, networks and interfaces (i.e. +an IP address associated with a specific IP subnet). + +(Contributed by Google and Peter Moody in :pep:`3144`) + +lzma +---- + +The newly-added :mod:`lzma` module provides data compression and decompression +using the LZMA algorithm, including support for the ``.xz`` and ``.lzma`` +file formats. + +(Contributed by Nadeem Vawda and Per Øyvind Karlsen in :issue:`6715`) + + +Improved Modules +================ + +abc +--- + +Improved support for abstract base classes containing descriptors composed with +abstract methods. The recommended approach to declaring abstract descriptors is +now to provide :attr:`__isabstractmethod__` as a dynamically updated +property. The built-in descriptors have been updated accordingly. + + * :class:`abc.abstractproperty` has been deprecated, use :class:`property` + with :func:`abc.abstractmethod` instead. + * :class:`abc.abstractclassmethod` has been deprecated, use + :class:`classmethod` with :func:`abc.abstractmethod` instead. + * :class:`abc.abstractstaticmethod` has been deprecated, use + :class:`staticmethod` with :func:`abc.abstractmethod` instead. + +(Contributed by Darren Dale in :issue:`11610`) + +:meth:`abc.ABCMeta.register` now returns the registered subclass, which means +it can now be used as a class decorator (:issue:`10868`). + + +array +----- + +The :mod:`array` module supports the :c:type:`long long` type using ``q`` and +``Q`` type codes. + +(Contributed by Oren Tirosh and Hirokazu Yamamoto in :issue:`1172711`) + + +base64 +------ + +ASCII-only Unicode strings are now accepted by the decoding functions of the +:mod:`base64` modern interface. For example, ``base64.b64decode('YWJj')`` +returns ``b'abc'``. (Contributed by Catalin Iacob in :issue:`13641`.) + + +binascii +-------- + +In addition to the binary objects they normally accept, the ``a2b_`` functions +now all also accept ASCII-only strings as input. (Contributed by Antoine +Pitrou in :issue:`13637`.) + + +bz2 +--- + +The :mod:`bz2` module has been rewritten from scratch. In the process, several +new features have been added: + +* New :func:`bz2.open` function: open a bzip2-compressed file in binary or + text mode. + +* :class:`bz2.BZ2File` can now read from and write to arbitrary file-like + objects, by means of its constructor's *fileobj* argument. + + (Contributed by Nadeem Vawda in :issue:`5863`) + +* :class:`bz2.BZ2File` and :func:`bz2.decompress` can now decompress + multi-stream inputs (such as those produced by the :program:`pbzip2` tool). + :class:`bz2.BZ2File` can now also be used to create this type of file, using + the ``'a'`` (append) mode. + + (Contributed by Nir Aides in :issue:`1625`) + +* :class:`bz2.BZ2File` now implements all of the :class:`io.BufferedIOBase` API, + except for the :meth:`detach` and :meth:`truncate` methods. + + +codecs +------ + +The :mod:`~encodings.mbcs` codec has been rewritten to handle correctly +``replace`` and ``ignore`` error handlers on all Windows versions. The +:mod:`~encodings.mbcs` codec now supports all error handlers, instead of only +``replace`` to encode and ``ignore`` to decode. + +A new Windows-only codec has been added: ``cp65001`` (:issue:`13216`). It is the +Windows code page 65001 (Windows UTF-8, ``CP_UTF8``). For example, it is used +by ``sys.stdout`` if the console output code page is set to cp65001 (e.g., using +``chcp 65001`` command). + +Multibyte CJK decoders now resynchronize faster. They only ignore the first +byte of an invalid byte sequence. For example, ``b'\xff\n'.decode('gb2312', +'replace')`` now returns a ``\n`` after the replacement character. + +(:issue:`12016`) + +Incremental CJK codec encoders are no longer reset at each call to their +encode() methods. For example:: + + $ ./python -q + >>> import codecs + >>> encoder = codecs.getincrementalencoder('hz')('strict') + >>> b''.join(encoder.encode(x) for x in '\u52ff\u65bd\u65bc\u4eba\u3002 Bye.') + b'~{NpJ)l6HK!#~} Bye.' + +This example gives ``b'~{Np~}~{J)~}~{l6~}~{HK~}~{!#~} Bye.'`` with older Python +versions. + +(:issue:`12100`) + +The ``unicode_internal`` codec has been deprecated. + + +collections +----------- + +Addition of a new :class:`~collections.ChainMap` class to allow treating a +number of mappings as a single unit. (Written by Raymond Hettinger for +:issue:`11089`, made public in :issue:`11297`) + +The abstract base classes have been moved in a new :mod:`collections.abc` +module, to better differentiate between the abstract and the concrete +collections classes. Aliases for ABCs are still present in the +:mod:`collections` module to preserve existing imports. (:issue:`11085`) + +.. XXX addition of __slots__ to ABCs not recorded here: internal detail + +The :class:`~collections.Counter` class now supports the unary ``+`` and ``-`` +operators, as well as the in-place operators ``+=``, ``-=``, ``|=``, and +``&=``. (Contributed by Raymond Hettinger in :issue:`13121`.) + + +contextlib +---------- + +:class:`~contextlib.ExitStack` now provides a solid foundation for +programmatic manipulation of context managers and similar cleanup +functionality. Unlike the previous ``contextlib.nested`` API (which was +deprecated and removed), the new API is designed to work correctly +regardless of whether context managers acquire their resources in +their ``__init__`` method (for example, file objects) or in their +``__enter__`` method (for example, synchronisation objects from the +:mod:`threading` module). + +(:issue:`13585`) + + +crypt +----- + +Addition of salt and modular crypt format (hashing method) and the :func:`~crypt.mksalt` +function to the :mod:`crypt` module. + +(:issue:`10924`) + +curses +------ + + * If the :mod:`curses` module is linked to the ncursesw library, use Unicode + functions when Unicode strings or characters are passed (e.g. + :c:func:`waddwstr`), and bytes functions otherwise (e.g. :c:func:`waddstr`). + * Use the locale encoding instead of ``utf-8`` to encode Unicode strings. + * :class:`curses.window` has a new :attr:`curses.window.encoding` attribute. + * The :class:`curses.window` class has a new :meth:`~curses.window.get_wch` + method to get a wide character + * The :mod:`curses` module has a new :meth:`~curses.unget_wch` function to + push a wide character so the next :meth:`~curses.window.get_wch` will return + it + +(Contributed by Iñigo Serna in :issue:`6755`) + +datetime +-------- + + * Equality comparisons between naive and aware :class:`~datetime.datetime` + instances now return :const:`False` instead of raising :exc:`TypeError` + (:issue:`15006`). + * New :meth:`datetime.datetime.timestamp` method: Return POSIX timestamp + corresponding to the :class:`~datetime.datetime` instance. + * The :meth:`datetime.datetime.strftime` method supports formatting years + older than 1000. + * The :meth:`datetime.datetime.astimezone` method can now be + called without arguments to convert datetime instance to the system + timezone. + + +.. _new-decimal: + +decimal +------- + +:issue:`7652` - integrate fast native decimal arithmetic. + C-module and libmpdec written by Stefan Krah. + +The new C version of the decimal module integrates the high speed libmpdec +library for arbitrary precision correctly-rounded decimal floating point +arithmetic. libmpdec conforms to IBM's General Decimal Arithmetic Specification. + +Performance gains range from 10x for database applications to 100x for +numerically intensive applications. These numbers are expected gains +for standard precisions used in decimal floating point arithmetic. Since +the precision is user configurable, the exact figures may vary. For example, +in integer bignum arithmetic the differences can be significantly higher. + +The following table is meant as an illustration. Benchmarks are available +at http://www.bytereef.org/mpdecimal/quickstart.html. + + +---------+-------------+--------------+-------------+ + | | decimal.py | _decimal | speedup | + +=========+=============+==============+=============+ + | pi | 42.02s | 0.345s | 120x | + +---------+-------------+--------------+-------------+ + | telco | 172.19s | 5.68s | 30x | + +---------+-------------+--------------+-------------+ + | psycopg | 3.57s | 0.29s | 12x | + +---------+-------------+--------------+-------------+ + +Features +~~~~~~~~ + +* The :exc:`~decimal.FloatOperation` signal optionally enables stricter + semantics for mixing floats and Decimals. + +* If Python is compiled without threads, the C version automatically + disables the expensive thread local context machinery. In this case, + the variable :data:`~decimal.HAVE_THREADS` is set to False. + +API changes +~~~~~~~~~~~ + +* The C module has the following context limits, depending on the machine + architecture: + + +-------------------+---------------------+------------------------------+ + | | 32-bit | 64-bit | + +===================+=====================+==============================+ + | :const:`MAX_PREC` | :const:`425000000` | :const:`999999999999999999` | + +-------------------+---------------------+------------------------------+ + | :const:`MAX_EMAX` | :const:`425000000` | :const:`999999999999999999` | + +-------------------+---------------------+------------------------------+ + | :const:`MIN_EMIN` | :const:`-425000000` | :const:`-999999999999999999` | + +-------------------+---------------------+------------------------------+ + +* In the context templates (:class:`~decimal.DefaultContext`, + :class:`~decimal.BasicContext` and :class:`~decimal.ExtendedContext`) + the magnitude of :attr:`~decimal.Context.Emax` and + :attr:`~decimal.Context.Emin` has changed to :const:`999999`. + +* The :class:`~decimal.Decimal` constructor in decimal.py does not observe + the context limits and converts values with arbitrary exponents or precision + exactly. Since the C version has internal limits, the following scheme is + used: If possible, values are converted exactly, otherwise + :exc:`~decimal.InvalidOperation` is raised and the result is NaN. In the + latter case it is always possible to use :meth:`~decimal.Context.create_decimal` + in order to obtain a rounded or inexact value. + + +* The power function in decimal.py is always correctly-rounded. In the + C version, it is defined in terms of the correctly-rounded + :meth:`~decimal.Decimal.exp` and :meth:`~decimal.Decimal.ln` functions, + but the final result is only "almost always correctly rounded". + + +* In the C version, the context dictionary containing the signals is a + :class:`~collections.abc.MutableMapping`. For speed reasons, + :attr:`~decimal.Context.flags` and :attr:`~decimal.Context.traps` always + refer to the same :class:`~collections.abc.MutableMapping` that the context + was initialized with. If a new signal dictionary is assigned, + :attr:`~decimal.Context.flags` and :attr:`~decimal.Context.traps` + are updated with the new values, but they do not reference the RHS + dictionary. + + +* Pickling a :class:`~decimal.Context` produces a different output in order + to have a common interchange format for the Python and C versions. + + +* The order of arguments in the :class:`~decimal.Context` constructor has been + changed to match the order displayed by :func:`repr`. + + +* The ``watchexp`` parameter in the :meth:`~decimal.Decimal.quantize` method + is deprecated. + + +.. _new-email: + +email +----- + +Policy Framework +~~~~~~~~~~~~~~~~ + +The email package now has a :mod:`~email.policy` framework. A +:class:`~email.policy.Policy` is an object with several methods and properties +that control how the email package behaves. The primary policy for Python 3.3 +is the :class:`~email.policy.Compat32` policy, which provides backward +compatibility with the email package in Python 3.2. A ``policy`` can be +specified when an email message is parsed by a :mod:`~email.parser`, or when a +:class:`~email.message.Message` object is created, or when an email is +serialized using a :mod:`~email.generator`. Unless overridden, a policy passed +to a ``parser`` is inherited by all the ``Message`` object and sub-objects +created by the ``parser``. By default a ``generator`` will use the policy of +the ``Message`` object it is serializing. The default policy is +:data:`~email.policy.compat32`. + +The minimum set of controls implemented by all ``policy`` objects are: + + =============== ======================================================= + max_line_length The maximum length, excluding the linesep character(s), + individual lines may have when a ``Message`` is + serialized. Defaults to 78. + + linesep The character used to separate individual lines when a + ``Message`` is serialized. Defaults to ``\n``. + + cte_type ``7bit`` or ``8bit``. ``8bit`` applies only to a + ``Bytes`` ``generator``, and means that non-ASCII may + be used where allowed by the protocol (or where it + exists in the original input). + + raise_on_defect Causes a ``parser`` to raise error when defects are + encountered instead of adding them to the ``Message`` + object's ``defects`` list. + =============== ======================================================= + +A new policy instance, with new settings, is created using the +:meth:`~email.policy.Policy.clone` method of policy objects. ``clone`` takes +any of the above controls as keyword arguments. Any control not specified in +the call retains its default value. Thus you can create a policy that uses +``\r\n`` linesep characters like this:: + + mypolicy = compat32.clone(linesep='\r\n') + +Policies can be used to make the generation of messages in the format needed by +your application simpler. Instead of having to remember to specify +``linesep='\r\n'`` in all the places you call a ``generator``, you can specify +it once, when you set the policy used by the ``parser`` or the ``Message``, +whichever your program uses to create ``Message`` objects. On the other hand, +if you need to generate messages in multiple forms, you can still specify the +parameters in the appropriate ``generator`` call. Or you can have custom +policy instances for your different cases, and pass those in when you create +the ``generator``. + + +Provisional Policy with New Header API +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +While the policy framework is worthwhile all by itself, the main motivation for +introducing it is to allow the creation of new policies that implement new +features for the email package in a way that maintains backward compatibility +for those who do not use the new policies. Because the new policies introduce a +new API, we are releasing them in Python 3.3 as a :term:`provisional policy +<provisional package>`. Backwards incompatible changes (up to and including +removal of the code) may occur if deemed necessary by the core developers. + +The new policies are instances of :class:`~email.policy.EmailPolicy`, +and add the following additional controls: + + =============== ======================================================= + refold_source Controls whether or not headers parsed by a + :mod:`~email.parser` are refolded by the + :mod:`~email.generator`. It can be ``none``, ``long``, + or ``all``. The default is ``long``, which means that + source headers with a line longer than + ``max_line_length`` get refolded. ``none`` means no + line get refolded, and ``all`` means that all lines + get refolded. + + header_factory A callable that take a ``name`` and ``value`` and + produces a custom header object. + =============== ======================================================= + +The ``header_factory`` is the key to the new features provided by the new +policies. When one of the new policies is used, any header retrieved from +a ``Message`` object is an object produced by the ``header_factory``, and any +time you set a header on a ``Message`` it becomes an object produced by +``header_factory``. All such header objects have a ``name`` attribute equal +to the header name. Address and Date headers have additional attributes +that give you access to the parsed data of the header. This means you can now +do things like this:: + + >>> m = Message(policy=SMTP) + >>> m['To'] = 'Éric <foo@example.com>' + >>> m['to'] + 'Éric <foo@example.com>' + >>> m['to'].addresses + (Address(display_name='Éric', username='foo', domain='example.com'),) + >>> m['to'].addresses[0].username + 'foo' + >>> m['to'].addresses[0].display_name + 'Éric' + >>> m['Date'] = email.utils.localtime() + >>> m['Date'].datetime + datetime.datetime(2012, 5, 25, 21, 39, 24, 465484, tzinfo=datetime.timezone(datetime.timedelta(-1, 72000), 'EDT')) + >>> m['Date'] + 'Fri, 25 May 2012 21:44:27 -0400' + >>> print(m) + To: =?utf-8?q?=C3=89ric?= <foo@example.com> + Date: Fri, 25 May 2012 21:44:27 -0400 + +You will note that the unicode display name is automatically encoded as +``utf-8`` when the message is serialized, but that when the header is accessed +directly, you get the unicode version. This eliminates any need to deal with +the :mod:`email.header` :meth:`~email.header.decode_header` or +:meth:`~email.header.make_header` functions. + +You can also create addresses from parts:: + + >>> m['cc'] = [Group('pals', [Address('Bob', 'bob', 'example.com'), + ... Address('Sally', 'sally', 'example.com')]), + ... Address('Bonzo', addr_spec='bonz@laugh.com')] + >>> print(m) + To: =?utf-8?q?=C3=89ric?= <foo@example.com> + Date: Fri, 25 May 2012 21:44:27 -0400 + cc: pals: Bob <bob@example.com>, Sally <sally@example.com>;, Bonzo <bonz@laugh.com> + +Decoding to unicode is done automatically:: + + >>> m2 = message_from_string(str(m)) + >>> m2['to'] + 'Éric <foo@example.com>' + +When you parse a message, you can use the ``addresses`` and ``groups`` +attributes of the header objects to access the groups and individual +addresses:: + + >>> m2['cc'].addresses + (Address(display_name='Bob', username='bob', domain='example.com'), Address(display_name='Sally', username='sally', domain='example.com'), Address(display_name='Bonzo', username='bonz', domain='laugh.com')) + >>> m2['cc'].groups + (Group(display_name='pals', addresses=(Address(display_name='Bob', username='bob', domain='example.com'), Address(display_name='Sally', username='sally', domain='example.com')), Group(display_name=None, addresses=(Address(display_name='Bonzo', username='bonz', domain='laugh.com'),)) + +In summary, if you use one of the new policies, header manipulation works the +way it ought to: your application works with unicode strings, and the email +package transparently encodes and decodes the unicode to and from the RFC +standard Content Transfer Encodings. + +Other API Changes +~~~~~~~~~~~~~~~~~ + +New :class:`~email.parser.BytesHeaderParser`, added to the :mod:`~email.parser` +module to complement :class:`~email.parser.HeaderParser` and complete the Bytes +API. + +New utility functions: + + * :func:`~email.utils.format_datetime`: given a :class:`~datetime.datetime`, + produce a string formatted for use in an email header. + + * :func:`~email.utils.parsedate_to_datetime`: given a date string from + an email header, convert it into an aware :class:`~datetime.datetime`, + or a naive :class:`~datetime.datetime` if the offset is ``-0000``. + + * :func:`~email.utils.localtime`: With no argument, returns the + current local time as an aware :class:`~datetime.datetime` using the local + :class:`~datetime.timezone`. Given an aware :class:`~datetime.datetime`, + converts it into an aware :class:`~datetime.datetime` using the + local :class:`~datetime.timezone`. + + +ftplib +------ + +* :class:`ftplib.FTP` now accepts a ``source_address`` keyword argument to + specify the ``(host, port)`` to use as the source address in the bind call + when creating the outgoing socket. (Contributed by Giampaolo Rodolà + in :issue:`8594`.) + +* The :class:`~ftplib.FTP_TLS` class now provides a new + :func:`~ftplib.FTP_TLS.ccc` function to revert control channel back to + plaintext. This can be useful to take advantage of firewalls that know how + to handle NAT with non-secure FTP without opening fixed ports. (Contributed + by Giampaolo Rodolà in :issue:`12139`) + +* Added :meth:`ftplib.FTP.mlsd` method which provides a parsable directory + listing format and deprecates :meth:`ftplib.FTP.nlst` and + :meth:`ftplib.FTP.dir`. (Contributed by Giampaolo Rodolà in :issue:`11072`) + + +functools +--------- + +The :func:`functools.lru_cache` decorator now accepts a ``typed`` keyword +argument (that defaults to ``False`` to ensure that it caches values of +different types that compare equal in separate cache slots. (Contributed +by Raymond Hettinger in :issue:`13227`.) + + +gc +-- + +It is now possible to register callbacks invoked by the garbage collector +before and after collection using the new :data:`~gc.callbacks` list. + + +hmac +---- + +A new :func:`~hmac.compare_digest` function has been added to prevent side +channel attacks on digests through timing analysis. (Contributed by Nick +Coghlan and Christian Heimes in :issue:`15061`) + + +http +---- + +:class:`http.server.BaseHTTPRequestHandler` now buffers the headers and writes +them all at once when :meth:`~http.server.BaseHTTPRequestHandler.end_headers` is +called. A new method :meth:`~http.server.BaseHTTPRequestHandler.flush_headers` +can be used to directly manage when the accumlated headers are sent. +(Contributed by Andrew Schaaf in :issue:`3709`.) + +:class:`http.server` now produces valid ``HTML 4.01 strict`` output. +(Contributed by Ezio Melotti in :issue:`13295`.) + +:class:`http.client.HTTPResponse` now has a +:meth:`~http.client.HTTPResponse.readinto` method, which means it can be used +as a :class:`io.RawIOBase` class. (Contributed by John Kuhn in +:issue:`13464`.) + + +html +---- + +:class:`html.parser.HTMLParser` is now able to parse broken markup without +raising errors, therefore the *strict* argument of the constructor and the +:exc:`~html.parser.HTMLParseError` exception are now deprecated. +The ability to parse broken markup is the result of a number of bug fixes that +are also available on the latest bug fix releases of Python 2.7/3.2. +(Contributed by Ezio Melotti in :issue:`15114`, and :issue:`14538`, +:issue:`13993`, :issue:`13960`, :issue:`13358`, :issue:`1745761`, +:issue:`755670`, :issue:`13357`, :issue:`12629`, :issue:`1200313`, +:issue:`670664`, :issue:`13273`, :issue:`12888`, :issue:`7311`) + +A new :data:`~html.entities.html5` dictionary that maps HTML5 named character +references to the equivalent Unicode character(s) (e.g. ``html5['gt;'] == +'>'``) has been added to the :mod:`html.entities` module. The dictionary is +now also used by :class:`~html.parser.HTMLParser`. (Contributed by Ezio +Melotti in :issue:`11113` and :issue:`15156`) + + +imaplib +------- + +The :class:`~imaplib.IMAP4_SSL` constructor now accepts an SSLContext +parameter to control parameters of the secure channel. + +(Contributed by Sijin Joseph in :issue:`8808`) + + +inspect +------- + +A new :func:`~inspect.getclosurevars` function has been added. This function +reports the current binding of all names referenced from the function body and +where those names were resolved, making it easier to verify correct internal +state when testing code that relies on stateful closures. + +(Contributed by Meador Inge and Nick Coghlan in :issue:`13062`) + +A new :func:`~inspect.getgeneratorlocals` function has been added. This +function reports the current binding of local variables in the generator's +stack frame, making it easier to verify correct internal state when testing +generators. + +(Contributed by Meador Inge in :issue:`15153`) + +io +-- + +The :func:`~io.open` function has a new ``'x'`` mode that can be used to +exclusively create a new file, and raise a :exc:`FileExistsError` if the file +already exists. It is based on the C11 'x' mode to fopen(). + +(Contributed by David Townshend in :issue:`12760`) + +The constructor of the :class:`~io.TextIOWrapper` class has a new +*write_through* optional argument. If *write_through* is ``True``, calls to +:meth:`~io.TextIOWrapper.write` are guaranteed not to be buffered: any data +written on the :class:`~io.TextIOWrapper` object is immediately handled to its +underlying binary buffer. + + +itertools +--------- + +:func:`~itertools.accumulate` now takes an optional ``func`` argument for +providing a user-supplied binary function. + + +logging +------- + +The :func:`~logging.basicConfig` function now supports an optional ``handlers`` +argument taking an iterable of handlers to be added to the root logger. + +A class level attribute :attr:`~logging.handlers.SysLogHandler.append_nul` has +been added to :class:`~logging.handlers.SysLogHandler` to allow control of the +appending of the ``NUL`` (``\000``) byte to syslog records, since for some +deamons it is required while for others it is passed through to the log. + + + +math +---- + +The :mod:`math` module has a new function, :func:`~math.log2`, which returns +the base-2 logarithm of *x*. + +(Written by Mark Dickinson in :issue:`11888`). + + +mmap +---- + +The :meth:`~mmap.mmap.read` method is now more compatible with other file-like +objects: if the argument is omitted or specified as ``None``, it returns the +bytes from the current file position to the end of the mapping. (Contributed +by Petri Lehtinen in :issue:`12021`.) + + +multiprocessing +--------------- + +The new :func:`multiprocessing.connection.wait` function allows to poll +multiple objects (such as connections, sockets and pipes) with a timeout. +(Contributed by Richard Oudkerk in :issue:`12328`.) + +:class:`multiprocessing.Connection` objects can now be transferred over +multiprocessing connections. +(Contributed by Richard Oudkerk in :issue:`4892`.) + +:class:`multiprocessing.Process` now accepts a ``daemon`` keyword argument +to override the default behavior of inheriting the ``daemon`` flag from +the parent process (:issue:`6064`). + +New attribute attribute :data:`multiprocessing.Process.sentinel` allows a +program to wait on multiple :class:`~multiprocessing.Process` objects at one +time using the appropriate OS primitives (for example, :mod:`select` on +posix systems). + +New methods :meth:`multiprocessing.pool.Pool.starmap` and +:meth:`~multiprocessing.pool.Pool.starmap_async` provide +:func:`itertools.starmap` equivalents to the existing +:meth:`multiprocessing.pool.Pool.map` and +:meth:`~multiprocessing.pool.Pool.map_async` functions. (Contributed by Hynek +Schlawack in :issue:`12708`.) + + +nntplib +------- + +The :class:`nntplib.NNTP` class now supports the context manager protocol to +unconditionally consume :exc:`socket.error` exceptions and to close the NNTP +connection when done:: + + >>> from nntplib import NNTP + >>> with NNTP('news.gmane.org') as n: + ... n.group('gmane.comp.python.committers') + ... + ('211 1755 1 1755 gmane.comp.python.committers', 1755, 1, 1755, 'gmane.comp.python.committers') + >>> + +(Contributed by Giampaolo Rodolà in :issue:`9795`) + + +os +-- + +* The :mod:`os` module has a new :func:`~os.pipe2` function that makes it + possible to create a pipe with :data:`~os.O_CLOEXEC` or + :data:`~os.O_NONBLOCK` flags set atomically. This is especially useful to + avoid race conditions in multi-threaded programs. + +* The :mod:`os` module has a new :func:`~os.sendfile` function which provides + an efficent "zero-copy" way for copying data from one file (or socket) + descriptor to another. The phrase "zero-copy" refers to the fact that all of + the copying of data between the two descriptors is done entirely by the + kernel, with no copying of data into userspace buffers. :func:`~os.sendfile` + can be used to efficiently copy data from a file on disk to a network socket, + e.g. for downloading a file. + + (Patch submitted by Ross Lagerwall and Giampaolo Rodolà in :issue:`10882`.) + +* To avoid race conditions like symlink attacks and issues with temporary + files and directories, it is more reliable (and also faster) to manipulate + file descriptors instead of file names. Python 3.3 enhances existing functions + and introduces new functions to work on file descriptors (:issue:`4761`, + :issue:`10755` and :issue:`14626`). + + - The :mod:`os` module has a new :func:`~os.fwalk` function similar to + :func:`~os.walk` except that it also yields file descriptors referring to the + directories visited. This is especially useful to avoid symlink races. + + - The following functions get new optional *dir_fd* (:ref:`paths relative to + directory descriptors <dir_fd>`) and/or *follow_symlinks* (:ref:`not + following symlinks <follow_symlinks>`): + :func:`~os.access`, :func:`~os.chflags`, :func:`~os.chmod`, :func:`~os.chown`, + :func:`~os.link`, :func:`~os.lstat`, :func:`~os.mkdir`, :func:`~os.mkfifo`, + :func:`~os.mknod`, :func:`~os.open`, :func:`~os.readlink`, :func:`~os.remove`, + :func:`~os.rename`, :func:`~os.replace`, :func:`~os.rmdir`, :func:`~os.stat`, + :func:`~os.symlink`, :func:`~os.unlink`, :func:`~os.utime`. Platform + support for using these parameters can be checked via the sets + :data:`os.supports_dir_fd` and :data:`os.supports_follows_symlinks`. + + - The following functions now support a file descriptor for their path argument: + :func:`~os.chdir`, :func:`~os.chmod`, :func:`~os.chown`, + :func:`~os.execve`, :func:`~os.listdir`, :func:`~os.pathconf`, :func:`~os.path.exists`, + :func:`~os.stat`, :func:`~os.statvfs`, :func:`~os.utime`. Platform support + for this can be checked via the :data:`os.supports_fd` set. + +* :func:`~os.access` accepts an ``effective_ids`` keyword argument to turn on + using the effective uid/gid rather than the real uid/gid in the access check. + Platform support for this can be checked via the + :data:`~os.supports_effective_ids` set. + +* The :mod:`os` module has two new functions: :func:`~os.getpriority` and + :func:`~os.setpriority`. They can be used to get or set process + niceness/priority in a fashion similar to :func:`os.nice` but extended to all + processes instead of just the current one. + + (Patch submitted by Giampaolo Rodolà in :issue:`10784`.) + +* The new :func:`os.replace` function allows cross-platform renaming of a + file with overwriting the destination. With :func:`os.rename`, an existing + destination file is overwritten under POSIX, but raises an error under + Windows. + (Contributed by Antoine Pitrou in :issue:`8828`.) + +* The stat family of functions (:func:`~os.stat`, :func:`~os.fstat`, + and :func:`~os.lstat`) now support reading a file's timestamps + with nanosecond precision. Symmetrically, :func:`~os.utime` + can now write file timestamps with nanosecond precision. (Contributed by + Larry Hastings in :issue:`14127`.) + +* The new :func:`os.get_terminal_size` function queries the size of the + terminal attached to a file descriptor. See also + :func:`shutil.get_terminal_size`. + (Contributed by Zbigniew Jędrzejewski-Szmek in :issue:`13609`.) + +.. XXX sort out this mess after beta1 + +* New functions to support Linux extended attributes (:issue:`12720`): + :func:`~os.getxattr`, :func:`~os.listxattr`, :func:`~os.removexattr`, + :func:`~os.setxattr`. + +* New interface to the scheduler. These functions + control how a process is allocated CPU time by the operating system. New + functions: + :func:`~os.sched_get_priority_max`, :func:`~os.sched_get_priority_min`, + :func:`~os.sched_getaffinity`, :func:`~os.sched_getparam`, + :func:`~os.sched_getscheduler`, :func:`~os.sched_rr_get_interval`, + :func:`~os.sched_setaffinity`, :func:`~os.sched_setparam`, + :func:`~os.sched_setscheduler`, :func:`~os.sched_yield`, + +* New functions to control the file system: + + * :func:`~os.posix_fadvise`: Announces an intention to access data in a + specific pattern thus allowing the kernel to make optimizations. + * :func:`~os.posix_fallocate`: Ensures that enough disk space is allocated + for a file. + * :func:`~os.sync`: Force write of everything to disk. + +* Additional new posix functions: + + * :func:`~os.lockf`: Apply, test or remove a POSIX lock on an open file descriptor. + * :func:`~os.pread`: Read from a file descriptor at an offset, the file + offset remains unchanged. + * :func:`~os.pwrite`: Write to a file descriptor from an offset, leaving + the file offset unchanged. + * :func:`~os.readv`: Read from a file descriptor into a number of writable buffers. + * :func:`~os.truncate`: Truncate the file corresponding to *path*, so that + it is at most *length* bytes in size. + * :func:`~os.waitid`: Wait for the completion of one or more child processes. + * :func:`~os.writev`: Write the contents of *buffers* to a file descriptor, + where *buffers* is an arbitrary sequence of buffers. + * :func:`~os.getgrouplist` (:issue:`9344`): Return list of group ids that + specified user belongs to. + +* :func:`~os.times` and :func:`~os.uname`: Return type changed from a tuple to + a tuple-like object with named attributes. + +* Some platforms now support additional constants for the :func:`~os.lseek` + function, such as ``os.SEEK_HOLE`` and ``os.SEEK_DATA``. + +* New constants :data:`~os.RTLD_LAZY`, :data:`~os.RTLD_NOW`, + :data:`~os.RTLD_GLOBAL`, :data:`~os.RTLD_LOCAL`, :data:`~os.RTLD_NODELETE`, + :data:`~os.RTLD_NOLOAD`, and :data:`~os.RTLD_DEEPBIND` are available on + platforms that support them. These are for use with the + :func:`sys.setdlopenflags` function, and supersede the similar constants + defined in :mod:`ctypes` and :mod:`DLFCN`. (Contributed by Victor Stinner + in :issue:`13226`.) + +* :func:`os.symlink` now accepts (and ignores) the ``target_is_directory`` + keyword argument on non-Windows platforms, to ease cross-platform support. + + +pdb +--- + +Tab-completion is now available not only for command names, but also their +arguments. For example, for the ``break`` command, function and file names +are completed. + +(Contributed by Georg Brandl in :issue:`14210`) + + +pickle +------ + +:class:`pickle.Pickler` objects now have an optional +:attr:`~pickle.Pickler.dispatch_table` attribute allowing to set per-pickler +reduction functions. + +(Contributed by Richard Oudkerk in :issue:`14166`.) + + +pydoc +----- + +The Tk GUI and the :func:`~pydoc.serve` function have been removed from the +:mod:`pydoc` module: ``pydoc -g`` and :func:`~pydoc.serve` have been deprecated +in Python 3.2. + + +re +-- + +:class:`str` regular expressions now support ``\u`` and ``\U`` escapes. + +(Contributed by Serhiy Storchaka in :issue:`3665`.) + + +sched +----- + +* :meth:`~sched.scheduler.run` now accepts a *blocking* parameter which when + set to False makes the method execute the scheduled events due to expire + soonest (if any) and then return immediately. + This is useful in case you want to use the :class:`~sched.scheduler` in + non-blocking applications. (Contributed by Giampaolo Rodolà in :issue:`13449`) + +* :class:`~sched.scheduler` class can now be safely used in multi-threaded + environments. (Contributed by Josiah Carlson and Giampaolo Rodolà in + :issue:`8684`) + +* *timefunc* and *delayfunct* parameters of :class:`~sched.scheduler` class + constructor are now optional and defaults to :func:`time.time` and + :func:`time.sleep` respectively. (Contributed by Chris Clark in + :issue:`13245`) + +* :meth:`~sched.scheduler.enter` and :meth:`~sched.scheduler.enterabs` + *argument* parameter is now optional. (Contributed by Chris Clark in + :issue:`13245`) + +* :meth:`~sched.scheduler.enter` and :meth:`~sched.scheduler.enterabs` + now accept a *kwargs* parameter. (Contributed by Chris Clark in + :issue:`13245`) + + +select +------ + +Solaris and derivatives platforms have a new class :class:`select.devpoll` +for high performance asynchronous sockets via :file:`/dev/poll`. +(Contributed by Jesús Cea Avión in :issue:`6397`.) + + +shlex +----- + +The previously undocumented helper function ``quote`` from the +:mod:`pipes` modules has been moved to the :mod:`shlex` module and +documented. :func:`~shlex.quote` properly escapes all characters in a string +that might be otherwise given special meaning by the shell. + + +shutil +------ + +* New functions: + + * :func:`~shutil.disk_usage`: provides total, used and free disk space + statistics. (Contributed by Giampaolo Rodolà in :issue:`12442`) + * :func:`~shutil.chown`: allows one to change user and/or group of the given + path also specifying the user/group names and not only their numeric + ids. (Contributed by Sandro Tosi in :issue:`12191`) + * :func:`shutil.get_terminal_size`: returns the size of the terminal window + to which the interpreter is attached. (Contributed by Zbigniew + Jędrzejewski-Szmek in :issue:`13609`.) + +* :func:`~shutil.copy2` and :func:`~shutil.copystat` now preserve file + timestamps with nanosecond precision on platforms that support it. + They also preserve file "extended attributes" on Linux. (Contributed + by Larry Hastings in :issue:`14127` and :issue:`15238`.) + +* Several functions now take an optional ``symlinks`` argument: when that + parameter is true, symlinks aren't dereferenced and the operation instead + acts on the symlink itself (or creates one, if relevant). + (Contributed by Hynek Schlawack in :issue:`12715`.) + +* When copying files to a different file system, :func:`~shutil.move` now + handles symlinks the way the posix ``mv`` command does, recreating the + symlink rather than copying the target file contents. (Contributed by + Jonathan Niehof in :issue:`9993`.) :func:`~shutil.move` now also returns + the ``dst`` argument as its result. + +* :func:`~shutil.rmtree` is now resistant to symlink attacks on platforms + which support the new ``dir_fd`` parameter in :func:`os.open` and + :func:`os.unlink`. (Contributed by Martin von Löwis and Hynek Schlawack + in :issue:`4489`.) + + +signal +------ + +* The :mod:`signal` module has new functions: + + * :func:`~signal.pthread_sigmask`: fetch and/or change the signal mask of the + calling thread (Contributed by Jean-Paul Calderone in :issue:`8407`) ; + * :func:`~signal.pthread_kill`: send a signal to a thread ; + * :func:`~signal.sigpending`: examine pending functions ; + * :func:`~signal.sigwait`: wait a signal. + * :func:`~signal.sigwaitinfo`: wait for a signal, returning detailed + information about it. + * :func:`~signal.sigtimedwait`: like :func:`~signal.sigwaitinfo` but with a + timeout. + +* The signal handler writes the signal number as a single byte instead of + a nul byte into the wakeup file descriptor. So it is possible to wait more + than one signal and know which signals were raised. + +* :func:`signal.signal` and :func:`signal.siginterrupt` raise an OSError, + instead of a RuntimeError: OSError has an errno attribute. + + +smtpd +----- + +The :mod:`smtpd` module now supports :rfc:`5321` (extended SMTP) and :rfc:`1870` +(size extension). Per the standard, these extensions are enabled if and only +if the client initiates the session with an ``EHLO`` command. + +(Initial ``ELHO`` support by Alberto Trevino. Size extension by Juhana +Jauhiainen. Substantial additional work on the patch contributed by Michele +Orrù and Dan Boswell. :issue:`8739`) + + +smtplib +------- + +The :class:`~smtplib.SMTP`, :class:`~smtplib.SMTP_SSL`, and +:class:`~smtplib.LMTP` classes now accept a ``source_address`` keyword argument +to specify the ``(host, port)`` to use as the source address in the bind call +when creating the outgoing socket. (Contributed by Paulo Scardine in +:issue:`11281`.) + +:class:`~smtplib.SMTP` now supports the context manager protocol, allowing an +``SMTP`` instance to be used in a ``with`` statement. (Contributed +by Giampaolo Rodolà in :issue:`11289`.) + +The :class:`~smtplib.SMTP_SSL` constructor and the :meth:`~smtplib.SMTP.starttls` +method now accept an SSLContext parameter to control parameters of the secure +channel. (Contributed by Kasun Herath in :issue:`8809`) + + +socket +------ + +* The :class:`~socket.socket` class now exposes additional methods to process + ancillary data when supported by the underlying platform: + + * :func:`~socket.socket.sendmsg` + * :func:`~socket.socket.recvmsg` + * :func:`~socket.socket.recvmsg_into` + + (Contributed by David Watson in :issue:`6560`, based on an earlier patch by + Heiko Wundram) + +* The :class:`~socket.socket` class now supports the PF_CAN protocol family + (http://en.wikipedia.org/wiki/Socketcan), on Linux + (http://lwn.net/Articles/253425). + + (Contributed by Matthias Fuchs, updated by Tiago Gonçalves in :issue:`10141`) + +* The :class:`~socket.socket` class now supports the PF_RDS protocol family + (http://en.wikipedia.org/wiki/Reliable_Datagram_Sockets and + http://oss.oracle.com/projects/rds/). + +* The :class:`~socket.socket` class now supports the ``PF_SYSTEM`` protocol + family on OS X. (Contributed by Michael Goderbauer in :issue:`13777`.) + +* New function :func:`~socket.sethostname` allows the hostname to be set + on unix systems if the calling process has sufficient privileges. + (Contributed by Ross Lagerwall in :issue:`10866`.) + + +socketserver +------------ + +:class:`~socketserver.BaseServer` now has an overridable method +:meth:`~socketserver.BaseServer.service_actions` that is called by the +:meth:`~socketserver.BaseServer.serve_forever` method in the service loop. +:class:`~socketserver.ForkingMixIn` now uses this to clean up zombie +child proceses. (Contributed by Justin Warkentin in :issue:`11109`.) + + +sqlite3 +------- + +New :class:`sqlite3.Connection` method +:meth:`~sqlite3.Connection.set_trace_callback` can be used to capture a trace of +all sql commands processed by sqlite. (Contributed by Torsten Landschoff +in :issue:`11688`.) + + +ssl +--- + +* The :mod:`ssl` module has two new random generation functions: + + * :func:`~ssl.RAND_bytes`: generate cryptographically strong + pseudo-random bytes. + * :func:`~ssl.RAND_pseudo_bytes`: generate pseudo-random bytes. + + (Contributed by Victor Stinner in :issue:`12049`) + +* The :mod:`ssl` module now exposes a finer-grained exception hierarchy + in order to make it easier to inspect the various kinds of errors. + (Contributed by Antoine Pitrou in :issue:`11183`) + +* :meth:`~ssl.SSLContext.load_cert_chain` now accepts a *password* argument + to be used if the private key is encrypted. + (Contributed by Adam Simpkins in :issue:`12803`) + +* Diffie-Hellman key exchange, both regular and Elliptic Curve-based, is + now supported through the :meth:`~ssl.SSLContext.load_dh_params` and + :meth:`~ssl.SSLContext.set_ecdh_curve` methods. + (Contributed by Antoine Pitrou in :issue:`13626` and :issue:`13627`) + +* SSL sockets have a new :meth:`~ssl.SSLSocket.get_channel_binding` method + allowing the implementation of certain authentication mechanisms such as + SCRAM-SHA-1-PLUS. (Contributed by Jacek Konieczny in :issue:`12551`) + +* You can query the SSL compression algorithm used by an SSL socket, thanks + to its new :meth:`~ssl.SSLSocket.compression` method. The new attribute + :attr:`~ssl.OP_NO_COMPRESSION` can be used to disable compression. + (Contributed by Antoine Pitrou in :issue:`13634`) + +* Support has been added for the Next Procotol Negotiation extension using + the :meth:`ssl.SSLContext.set_npn_protocols` method. + (Contributed by Colin Marc in :issue:`14204`) + +* SSL errors can now be introspected more easily thanks to + :attr:`~ssl.SSLError.library` and :attr:`~ssl.SSLError.reason` attributes. + (Contributed by Antoine Pitrou in :issue:`14837`) + +* The :func:`~ssl.get_server_certificate` function now supports IPv6. + (Contributed by Charles-François Natali in :issue:`11811`.) + +* New attribute :attr:`~ssl.OP_CIPHER_SERVER_PREFERENCE` allows setting + SSLv3 server sockets to use the server's cipher ordering preference rather + than the client's (:issue:`13635`). + + +stat +---- + +The undocumented tarfile.filemode function has been moved to +:func:`stat.filemode`. It can be used to convert a file's mode to a string of +the form '-rwxrwxrwx'. + +(Contributed by Giampaolo Rodolà in :issue:`14807`) + + +struct +------ + +The :mod:`struct` module now supports ``ssize_t`` and ``size_t`` via the +new codes ``n`` and ``N``, respectively. (Contributed by Antoine Pitrou +in :issue:`3163`.) + + +subprocess +---------- + +Command strings can now be bytes objects on posix platforms. (Contributed by +Victor Stinner in :issue:`8513`.) + +A new constant :data:`~subprocess.DEVNULL` allows suppressing output in a +platform-independent fashion. (Contributed by Ross Lagerwall in +:issue:`5870`.) + + +sys +--- + +The :mod:`sys` module has a new :data:`~sys.thread_info` :term:`struct +sequence` holding informations about the thread implementation +(:issue:`11223`). + + +tarfile +------- + +:mod:`tarfile` now supports ``lzma`` encoding via the :mod:`lzma` module. +(Contributed by Lars Gustäbel in :issue:`5689`.) + + +tempfile +-------- + +:class:`tempfile.SpooledTemporaryFile`\'s +:meth:`~tempfile.SpooledTemporaryFile.trucate` method now accepts +a ``size`` parameter. (Contributed by Ryan Kelly in :issue:`9957`.) + + +textwrap +-------- + +The :mod:`textwrap` module has a new :func:`~textwrap.indent` that makes +it straightforward to add a common prefix to selected lines in a block +of text (:issue:`13857`). + + +threading +--------- + +:class:`threading.Condition`, :class:`threading.Semaphore`, +:class:`threading.BoundedSemaphore`, :class:`threading.Event`, and +:class:`threading.Timer`, all of which used to be factory functions returning a +class instance, are now classes and may be subclassed. (Contributed by Éric +Araujo in :issue:`10968`). + +The :class:`threading.Thread` constructor now accepts a ``daemon`` keyword +argument to override the default behavior of inheriting the ``deamon`` flag +value from the parent thread (:issue:`6064`). + +The formerly private function ``_thread.get_ident`` is now available as the +public function :func:`threading.get_ident`. This eliminates several cases of +direct access to the ``_thread`` module in the stdlib. Third party code that +used ``_thread.get_ident`` should likewise be changed to use the new public +interface. + + +time +---- + +The :pep:`418` added new functions to the :mod:`time` module: + +* :func:`~time.get_clock_info`: Get information on a clock. +* :func:`~time.monotonic`: Monotonic clock (cannot go backward), not affected + by system clock updates. +* :func:`~time.perf_counter`: Performance counter with the highest available + resolution to measure a short duration. +* :func:`~time.process_time`: Sum of the system and user CPU time of the + current process. + +Other new functions: + +* :func:`~time.clock_getres`, :func:`~time.clock_gettime` and + :func:`~time.clock_settime` functions with ``CLOCK_xxx`` constants. + (Contributed by Victor Stinner in :issue:`10278`) + +To improve cross platform consistency, :func:`~time.sleep` now raises a +:exc:`ValueError` when passed a negative sleep value. Previously this was an +error on posix, but produced an infinite sleep on Windows. + + +types +----- + +Add a new :class:`types.MappingProxyType` class: Read-only proxy of a mapping. +(:issue:`14386`) + + +The new functions `types.new_class` and `types.prepare_class` provide support +for PEP 3115 compliant dynamic type creation. (:issue:`14588`) + + +unittest +-------- + +:meth:`.assertRaises`, :meth:`.assertRaisesRegex`, :meth:`.assertWarns`, and +:meth:`.assertWarnsRegex` now accept a keyword argument *msg* when used as +context managers. (Contributed by Ezio Melotti and Winston Ewert in +:issue:`10775`) + +:meth:`unittest.TestCase.run` now returns the :class:`~unittest.TestResult` +object. + + +urllib +------ + +The :class:`~urllib.request.Request` class, now accepts a *method* argument +used by :meth:`~urllib.request.Request.get_method` to determine what HTTP method +should be used. For example, this will send a ``'HEAD'`` request:: + + >>> urlopen(Request('http://www.python.org', method='HEAD')) + +(:issue:`1673007`) + + +webbrowser +---------- + +The :mod:`webbrowser` module supports more "browsers": Google Chrome (named +:program:`chrome`, :program:`chromium`, :program:`chrome-browser` or +:program:`chromium-browser` depending on the version and operating system), +and the generic launchers :program:`xdg-open`, from the FreeDesktop.org +project, and :program:`gvfs-open`, which is the default URI handler for GNOME +3. (The former contributed by Arnaud Calmettes in :issue:`13620`, the latter +by Matthias Klose in :issue:`14493`) + + +xml.etree.ElementTree +--------------------- + +The :mod:`xml.etree.ElementTree` module now imports its C accelerator by +default; there is no longer a need to explicitly import +:mod:`xml.etree.cElementTree` (this module stays for backwards compatibility, +but is now deprecated). In addition, the ``iter`` family of methods of +:class:`~xml.etree.ElementTree.Element` has been optimized (rewritten in C). +The module's documentation has also been greatly improved with added examples +and a more detailed reference. + + +zlib +---- + +New attribute :attr:`zlib.Decompress.eof` makes it possible to distinguish +between a properly-formed compressed stream and an incomplete or truncated one. +(Contributed by Nadeem Vawda in :issue:`12646`.) + +New attribute :attr:`zlib.ZLIB_RUNTIME_VERSION` reports the version string of +the underlying ``zlib`` library that is loaded at runtime. (Contributed by +Torsten Landschoff in :issue:`12306`.) + + +Optimizations +============= + +Major performance enhancements have been added: + +* Thanks to :pep:`393`, some operations on Unicode strings have been optimized: + + * the memory footprint is divided by 2 to 4 depending on the text + * encode an ASCII string to UTF-8 doesn't need to encode characters anymore, + the UTF-8 representation is shared with the ASCII representation + * the UTF-8 encoder has been optimized + * repeating a single ASCII letter and getting a substring of a ASCII strings + is 4 times faster + +* UTF-8 is now 2x to 4x faster. UTF-16 encoding is now up to 10x faster. + + (contributed by Serhiy Storchaka, :issue:`14624`, :issue:`14738` and + :issue:`15026`.) + + +Build and C API Changes +======================= + +Changes to Python's build process and to the C API include: + +* New :pep:`3118` related function: + + * :c:func:`PyMemoryView_FromMemory` + +* :pep:`393` added new Unicode types, macros and functions: + + * High-level API: + + * :c:func:`PyUnicode_CopyCharacters` + * :c:func:`PyUnicode_FindChar` + * :c:func:`PyUnicode_GetLength`, :c:macro:`PyUnicode_GET_LENGTH` + * :c:func:`PyUnicode_New` + * :c:func:`PyUnicode_Substring` + * :c:func:`PyUnicode_ReadChar`, :c:func:`PyUnicode_WriteChar` + + * Low-level API: + + * :c:type:`Py_UCS1`, :c:type:`Py_UCS2`, :c:type:`Py_UCS4` types + * :c:type:`PyASCIIObject` and :c:type:`PyCompactUnicodeObject` structures + * :c:macro:`PyUnicode_READY` + * :c:func:`PyUnicode_FromKindAndData` + * :c:func:`PyUnicode_AsUCS4`, :c:func:`PyUnicode_AsUCS4Copy` + * :c:macro:`PyUnicode_DATA`, :c:macro:`PyUnicode_1BYTE_DATA`, + :c:macro:`PyUnicode_2BYTE_DATA`, :c:macro:`PyUnicode_4BYTE_DATA` + * :c:macro:`PyUnicode_KIND` with :c:type:`PyUnicode_Kind` enum: + :c:data:`PyUnicode_WCHAR_KIND`, :c:data:`PyUnicode_1BYTE_KIND`, + :c:data:`PyUnicode_2BYTE_KIND`, :c:data:`PyUnicode_4BYTE_KIND` + * :c:macro:`PyUnicode_READ`, :c:macro:`PyUnicode_READ_CHAR`, :c:macro:`PyUnicode_WRITE` + * :c:macro:`PyUnicode_MAX_CHAR_VALUE` + +* :c:macro:`PyArg_ParseTuple` now accepts a :class:`bytearray` for the ``c`` + format (:issue:`12380`). + + + +Deprecated +========== + +Unsupported Operating Systems +----------------------------- + +OS/2 and VMS are no longer supported due to the lack of a maintainer. + +Windows 2000 and Windows platforms which set ``COMSPEC`` to ``command.com`` +are no longer supported due to maintenance burden. + +OSF support, which was deprecated in 3.2, has been completely removed. + + +Deprecated Python modules, functions and methods +------------------------------------------------ + +* Passing a non-empty string to ``object.__format__()`` is deprecated, and + will produce a :exc:`TypeError` in Python 3.4 (:issue:`9856`). +* The ``unicode_internal`` codec has been deprecated because of the + :pep:`393`, use UTF-8, UTF-16 (``utf-16-le`` or ``utf-16-be``), or UTF-32 + (``utf-32-le`` or ``utf-32-be``) +* :meth:`ftplib.FTP.nlst` and :meth:`ftplib.FTP.dir`: use + :meth:`ftplib.FTP.mlsd` +* :func:`platform.popen`: use the :mod:`subprocess` module. Check especially + the :ref:`subprocess-replacements` section (:issue:`11377`). +* :issue:`13374`: The Windows bytes API has been deprecated in the :mod:`os` + module. Use Unicode filenames, instead of bytes filenames, to not depend on + the ANSI code page anymore and to support any filename. +* :issue:`13988`: The :mod:`xml.etree.cElementTree` module is deprecated. The + accelerator is used automatically whenever available. +* The behaviour of :func:`time.clock` depends on the platform: use the new + :func:`time.perf_counter` or :func:`time.process_time` function instead, + depending on your requirements, to have a well defined behaviour. +* The :func:`os.stat_float_times` function is deprecated. +* :mod:`abc` module: + + * :class:`abc.abstractproperty` has been deprecated, use :class:`property` + with :func:`abc.abstractmethod` instead. + * :class:`abc.abstractclassmethod` has been deprecated, use + :class:`classmethod` with :func:`abc.abstractmethod` instead. + * :class:`abc.abstractstaticmethod` has been deprecated, use + :class:`staticmethod` with :func:`abc.abstractmethod` instead. + +* :mod:`importlib` package: + + * :meth:`importlib.abc.SourceLoader.path_mtime` is now deprecated in favour of + :meth:`importlib.abc.SourceLoader.path_stats` as bytecode files now store + both the modification time and size of the source file the bytecode file was + compiled from. + + + + + +Deprecated functions and types of the C API +------------------------------------------- + +The :c:type:`Py_UNICODE` has been deprecated by :pep:`393` and will be +removed in Python 4. All functions using this type are deprecated: + +Unicode functions and methods using :c:type:`Py_UNICODE` and +:c:type:`Py_UNICODE*` types: + +* :c:macro:`PyUnicode_FromUnicode`: use :c:func:`PyUnicode_FromWideChar` or + :c:func:`PyUnicode_FromKindAndData` +* :c:macro:`PyUnicode_AS_UNICODE`, :c:func:`PyUnicode_AsUnicode`, + :c:func:`PyUnicode_AsUnicodeAndSize`: use :c:func:`PyUnicode_AsWideCharString` +* :c:macro:`PyUnicode_AS_DATA`: use :c:macro:`PyUnicode_DATA` with + :c:macro:`PyUnicode_READ` and :c:macro:`PyUnicode_WRITE` +* :c:macro:`PyUnicode_GET_SIZE`, :c:func:`PyUnicode_GetSize`: use + :c:macro:`PyUnicode_GET_LENGTH` or :c:func:`PyUnicode_GetLength` +* :c:macro:`PyUnicode_GET_DATA_SIZE`: use + ``PyUnicode_GET_LENGTH(str) * PyUnicode_KIND(str)`` (only work on ready + strings) +* :c:func:`PyUnicode_AsUnicodeCopy`: use :c:func:`PyUnicode_AsUCS4Copy` or + :c:func:`PyUnicode_AsWideCharString` +* :c:func:`PyUnicode_GetMax` + + +Functions and macros manipulating Py_UNICODE* strings: + +* :c:macro:`Py_UNICODE_strlen`: use :c:func:`PyUnicode_GetLength` or + :c:macro:`PyUnicode_GET_LENGTH` +* :c:macro:`Py_UNICODE_strcat`: use :c:func:`PyUnicode_CopyCharacters` or + :c:func:`PyUnicode_FromFormat` +* :c:macro:`Py_UNICODE_strcpy`, :c:macro:`Py_UNICODE_strncpy`, + :c:macro:`Py_UNICODE_COPY`: use :c:func:`PyUnicode_CopyCharacters` or + :c:func:`PyUnicode_Substring` +* :c:macro:`Py_UNICODE_strcmp`: use :c:func:`PyUnicode_Compare` +* :c:macro:`Py_UNICODE_strncmp`: use :c:func:`PyUnicode_Tailmatch` +* :c:macro:`Py_UNICODE_strchr`, :c:macro:`Py_UNICODE_strrchr`: use + :c:func:`PyUnicode_FindChar` +* :c:macro:`Py_UNICODE_FILL`: use :c:func:`PyUnicode_Fill` +* :c:macro:`Py_UNICODE_MATCH` + +Encoders: + +* :c:func:`PyUnicode_Encode`: use :c:func:`PyUnicode_AsEncodedObject` +* :c:func:`PyUnicode_EncodeUTF7` +* :c:func:`PyUnicode_EncodeUTF8`: use :c:func:`PyUnicode_AsUTF8` or + :c:func:`PyUnicode_AsUTF8String` +* :c:func:`PyUnicode_EncodeUTF32` +* :c:func:`PyUnicode_EncodeUTF16` +* :c:func:`PyUnicode_EncodeUnicodeEscape:` use + :c:func:`PyUnicode_AsUnicodeEscapeString` +* :c:func:`PyUnicode_EncodeRawUnicodeEscape:` use + :c:func:`PyUnicode_AsRawUnicodeEscapeString` +* :c:func:`PyUnicode_EncodeLatin1`: use :c:func:`PyUnicode_AsLatin1String` +* :c:func:`PyUnicode_EncodeASCII`: use :c:func:`PyUnicode_AsASCIIString` +* :c:func:`PyUnicode_EncodeCharmap` +* :c:func:`PyUnicode_TranslateCharmap` +* :c:func:`PyUnicode_EncodeMBCS`: use :c:func:`PyUnicode_AsMBCSString` or + :c:func:`PyUnicode_EncodeCodePage` (with ``CP_ACP`` code_page) +* :c:func:`PyUnicode_EncodeDecimal`, + :c:func:`PyUnicode_TransformDecimalToASCII` + + +Deprecated features +------------------- + +The :mod:`array` module's ``'u'`` format code is now deprecated and will be +removed in Python 4 together with the rest of the (:c:type:`Py_UNICODE`) API. + + +Porting to Python 3.3 +===================== + +This section lists previously described changes and other bugfixes +that may require changes to your code. + +.. _portingpythoncode: + +Porting Python code +------------------- + +* Hash randomization is enabled by default. Set the :envvar:`PYTHONHASHSEED` + environment variable to ``0`` to disable hash randomization. See also the + :meth:`object.__hash__` method. + +* :issue:`12326`: On Linux, sys.platform doesn't contain the major version + anymore. It is now always 'linux', instead of 'linux2' or 'linux3' depending + on the Linux version used to build Python. Replace sys.platform == 'linux2' + with sys.platform.startswith('linux'), or directly sys.platform == 'linux' if + you don't need to support older Python versions. + +* :issue:`13847`, :issue:`14180`: :mod:`time` and :mod:`datetime`: + :exc:`OverflowError` is now raised instead of :exc:`ValueError` if a + timestamp is out of range. :exc:`OSError` is now raised if C functions + :c:func:`gmtime` or :c:func:`localtime` failed. + +* The default finders used by import now utilize a cache of what is contained + within a specific directory. If you create a Python source file or sourceless + bytecode file, make sure to call :func:`importlib.invalidate_caches` to clear + out the cache for the finders to notice the new file. + +* :exc:`ImportError` now uses the full name of the module that was attemped to + be imported. Doctests that check ImportErrors' message will need to be + updated to use the full name of the module instead of just the tail of the + name. + +* The *index* argument to :func:`__import__` now defaults to 0 instead of -1 + and no longer support negative values. It was an oversight when :pep:`328` was + implemented that the default value remained -1. If you need to continue to + perform a relative import followed by an absolute import, then perform the + relative import using an index of 1, followed by another import using an + index of 0. It is preferred, though, that you use + :func:`importlib.import_module` rather than call :func:`__import__` directly. + +* :func:`__import__` no longer allows one to use an index value other than 0 + for top-level modules. E.g. ``__import__('sys', level=1)`` is now an error. + +* Because :attr:`sys.meta_path` and :attr:`sys.path_hooks` now have finders on + them by default, you will most likely want to use :meth:`list.insert` instead + of :meth:`list.append` to add to those lists. + +* Because ``None`` is now inserted into :attr:`sys.path_importer_cache`, if you + are clearing out entries in the dictionary of paths that do not have a + finder, you will need to remove keys paired with values of ``None`` **and** + :class:`imp.NullImporter` to be backwards-compatible. This will lead to extra + overhead on older versions of Python that re-insert ``None`` into + :attr:`sys.path_importer_cache` where it repesents the use of implicit + finders, but semantically it should not change anything. + +* :class:`importlib.abc.Finder` no longer specifies a `find_module()` abstract + method that must be implemented. If you were relying on subclasses to + implement that method, make sure to check for the method's existence first. + You will probably want to check for `find_loader()` first, though, in the + case of working with :term:`path entry finders <path entry finder>`. + +* :mod:`pkgutil` has been converted to use :mod:`importlib` internally. This + eliminates many edge cases where the old behaviour of the PEP 302 import + emulation failed to match the behaviour of the real import system. The + import emulation itself is still present, but is now deprecated. The + :func:`pkgutil.iter_importers` and :func:`pkgutil.walk_packages` functions + special case the standard import hooks so they are still supported even + though they do not provide the non-standard ``iter_modules()`` method. + +* A longstanding RFC-compliance bug (:issue:`1079`) in the parsing done by + :func:`email.header.decode_header` has been fixed. Code that uses the + standard idiom to convert encoded headers into unicode + (``str(make_header(decode_header(h))``) will see no change, but code that + looks at the individual tuples returned by decode_header will see that + whitespace that precedes or follows ``ASCII`` sections is now included in the + ``ASCII`` section. Code that builds headers using ``make_header`` should + also continue to work without change, since ``make_header`` continues to add + whitespace between ``ASCII`` and non-``ASCII`` sections if it is not already + present in the input strings. + +* :func:`email.utils.formataddr` now does the correct content transfer + encoding when passed non-``ASCII`` display names. Any code that depended on + the previous buggy behavior that preserved the non-``ASCII`` unicode in the + formatted output string will need to be changed (:issue:`1690608`). + +* :meth:`poplib.POP3.quit` may now raise protocol errors like all other + ``poplib`` methods. Code that assumes ``quit`` does not raise + :exc:`poplib.error_proto` errors may need to be changed if errors on ``quit`` + are encountered by a particular application (:issue:`11291`). + +* The ``strict`` argument to :class:`email.parser.Parser`, deprecated since + Python 2.4, has finally been removed. + +* The deprecated method ``unittest.TestCase.assertSameElements`` has been + removed. + +* The deprecated variable ``time.accept2dyear`` has been removed. + +* The deprecated ``Context._clamp`` attribute has been removed from the + :mod:`decimal` module. It was previously replaced by the public attribute + :attr:`~decimal.Context.clamp`. (See :issue:`8540`.) + +* The undocumented internal helper class ``SSLFakeFile`` has been removed + from :mod:`smtplib`, since its functionality has long been provided directly + by :meth:`socket.socket.makefile`. + +* Passing a negative value to :func:`time.sleep` on Windows now raises an + error instead of sleeping forever. It has always raised an error on posix. + +* The ``ast.__version__`` constant has been removed. If you need to + make decisions affected by the AST version, use :attr:`sys.version_info` + to make the decision. + +* Code that used to work around the fact that the :mod:`threading` module used + factory functions by subclassing the private classes will need to change to + subclass the now-public classes. + +* The undocumented debugging machinery in the threading module has been + removed, simplifying the code. This should have no effect on production + code, but is mentioned here in case any application debug frameworks were + interacting with it (:issue:`13550`). + + +Porting C code +-------------- + +* In the course of changes to the buffer API the undocumented + :c:member:`~Py_buffer.smalltable` member of the + :c:type:`Py_buffer` structure has been removed and the + layout of the :c:type:`PyMemoryViewObject` has changed. + + All extensions relying on the relevant parts in ``memoryobject.h`` + or ``object.h`` must be rebuilt. + +* Due to :ref:`PEP 393 <pep-393>`, the :c:type:`Py_UNICODE` type and all + functions using this type are deprecated (but will stay available for + at least five years). If you were using low-level Unicode APIs to + construct and access unicode objects and you want to benefit of the + memory footprint reduction provided by PEP 393, you have to convert + your code to the new :doc:`Unicode API <../c-api/unicode>`. + + However, if you only have been using high-level functions such as + :c:func:`PyUnicode_Concat()`, :c:func:`PyUnicode_Join` or + :c:func:`PyUnicode_FromFormat()`, your code will automatically take + advantage of the new unicode representations. + +* :c:func:`PyImport_GetMagicNumber` now returns -1 upon failure. + +* As a negative value for the *level* argument to :func:`__import__` is no + longer valid, the same now holds for :c:func:`PyImport_ImportModuleLevel`. + This also means that the value of *level* used by + :c:func:`PyImport_ImportModuleEx` is now 0 instead of -1. + + +Building C extensions +--------------------- + +* The range of possible file names for C extensions has been narrowed. + Very rarely used spellings have been suppressed: under POSIX, files + named ``xxxmodule.so``, ``xxxmodule.abi3.so`` and + ``xxxmodule.cpython-*.so`` are no longer recognized as implementing + the ``xxx`` module. If you had been generating such files, you have + to switch to the other spellings (i.e., remove the ``module`` string + from the file names). + + (implemented in :issue:`14040`.) + + +Command Line Switch Changes +--------------------------- + +* The -Q command-line flag and related artifacts have been removed. Code + checking sys.flags.division_warning will need updating. + + (:issue:`10998`, contributed by Éric Araujo.) + +* When :program:`python` is started with :option:`-S`, ``import site`` + will no longer add site-specific paths to the module search paths. In + previous versions, it did. + + (:issue:`11591`, contributed by Carl Meyer with editions by Éric Araujo.) |