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:mod:`py_compile` --- Compile Python source files
=================================================
.. module:: py_compile
:synopsis: Generate byte-code files from Python source files.
.. sectionauthor:: Fred L. Drake, Jr. <fdrake@acm.org>
.. documentation based on module docstrings
**Source code:** :source:`Lib/py_compile.py`
.. index:: pair: file; byte-code
--------------
The :mod:`py_compile` module provides a function to generate a byte-code file
from a source file, and another function used when the module source file is
invoked as a script.
Though not often needed, this function can be useful when installing modules for
shared use, especially if some of the users may not have permission to write the
byte-code cache files in the directory containing the source code.
.. exception:: PyCompileError
Exception raised when an error occurs while attempting to compile the file.
.. function:: compile(file, cfile=None, dfile=None, doraise=False, optimize=-1, invalidation_mode=PycInvalidationMode.TIMESTAMP)
Compile a source file to byte-code and write out the byte-code cache file.
The source code is loaded from the file named *file*. The byte-code is
written to *cfile*, which defaults to the :pep:`3147`/:pep:`488` path, ending
in ``.pyc``.
For example, if *file* is ``/foo/bar/baz.py`` *cfile* will default to
``/foo/bar/__pycache__/baz.cpython-32.pyc`` for Python 3.2. If *dfile* is
specified, it is used as the name of the source file in error messages when
instead of *file*. If *doraise* is true, a :exc:`PyCompileError` is raised
when an error is encountered while compiling *file*. If *doraise* is false
(the default), an error string is written to ``sys.stderr``, but no exception
is raised. This function returns the path to byte-compiled file, i.e.
whatever *cfile* value was used.
The *doraise* and *quiet* arguments determine how errors are handled while
compiling file. If *quiet* is 0 or 1, and *doraise* is false, the default
behaviour is enabled: an error string is written to ``sys.stderr``, and the
function returns ``None`` instead of a path. If *doraise* is true,
a :exc:`PyCompileError` is raised instead. However if *quiet* is 2,
no message is written, and *doraise* has no effect.
If the path that *cfile* becomes (either explicitly specified or computed)
is a symlink or non-regular file, :exc:`FileExistsError` will be raised.
This is to act as a warning that import will turn those paths into regular
files if it is allowed to write byte-compiled files to those paths. This is
a side-effect of import using file renaming to place the final byte-compiled
file into place to prevent concurrent file writing issues.
*optimize* controls the optimization level and is passed to the built-in
:func:`compile` function. The default of ``-1`` selects the optimization
level of the current interpreter.
*invalidation_mode* should be a member of the :class:`PycInvalidationMode`
enum and controls how the generated bytecode cache is invalidated at
runtime. The default is :attr:`PycInvalidationMode.CHECKED_HASH` if
the :envvar:`SOURCE_DATE_EPOCH` environment variable is set, otherwise
the default is :attr:`PycInvalidationMode.TIMESTAMP`.
.. versionchanged:: 3.2
Changed default value of *cfile* to be :PEP:`3147`-compliant. Previous
default was *file* + ``'c'`` (``'o'`` if optimization was enabled).
Also added the *optimize* parameter.
.. versionchanged:: 3.4
Changed code to use :mod:`importlib` for the byte-code cache file writing.
This means file creation/writing semantics now match what :mod:`importlib`
does, e.g. permissions, write-and-move semantics, etc. Also added the
caveat that :exc:`FileExistsError` is raised if *cfile* is a symlink or
non-regular file.
.. versionchanged:: 3.7
The *invalidation_mode* parameter was added as specified in :pep:`552`.
If the :envvar:`SOURCE_DATE_EPOCH` environment variable is set,
*invalidation_mode* will be forced to
:attr:`PycInvalidationMode.CHECKED_HASH`.
.. versionchanged:: 3.7.2
The :envvar:`SOURCE_DATE_EPOCH` environment variable no longer
overrides the value of the *invalidation_mode* argument, and determines
its default value instead.
.. versionchanged:: 3.8
The *quiet* parameter was added.
.. class:: PycInvalidationMode
A enumeration of possible methods the interpreter can use to determine
whether a bytecode file is up to date with a source file. The ``.pyc`` file
indicates the desired invalidation mode in its header. See
:ref:`pyc-invalidation` for more information on how Python invalidates
``.pyc`` files at runtime.
.. versionadded:: 3.7
.. attribute:: TIMESTAMP
The ``.pyc`` file includes the timestamp and size of the source file,
which Python will compare against the metadata of the source file at
runtime to determine if the ``.pyc`` file needs to be regenerated.
.. attribute:: CHECKED_HASH
The ``.pyc`` file includes a hash of the source file content, which Python
will compare against the source at runtime to determine if the ``.pyc``
file needs to be regenerated.
.. attribute:: UNCHECKED_HASH
Like :attr:`CHECKED_HASH`, the ``.pyc`` file includes a hash of the source
file content. However, Python will at runtime assume the ``.pyc`` file is
up to date and not validate the ``.pyc`` against the source file at all.
This option is useful when the ``.pycs`` are kept up to date by some
system external to Python like a build system.
.. function:: main(args=None)
Compile several source files. The files named in *args* (or on the command
line, if *args* is ``None``) are compiled and the resulting byte-code is
cached in the normal manner. This function does not search a directory
structure to locate source files; it only compiles files named explicitly.
If ``'-'`` is the only parameter in args, the list of files is taken from
standard input.
.. versionchanged:: 3.2
Added support for ``'-'``.
When this module is run as a script, the :func:`main` is used to compile all the
files named on the command line. The exit status is nonzero if one of the files
could not be compiled.
.. seealso::
Module :mod:`compileall`
Utilities to compile all Python source files in a directory tree.
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