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author | Guido van Rossum <guido@python.org> | 2020-04-24 11:25:10 -0700 |
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committer | Guido van Rossum <guido@python.org> | 2020-04-24 11:25:10 -0700 |
commit | 4a69b71a18ef6e228d8716ff33a9379d17e985fa (patch) | |
tree | 4e0cb59804293fc735bd2a19605ff6281af3c3a8 | |
parent | 24ffe705c30e36c82940d75fd1454256634d0b3c (diff) | |
download | cpython-git-whatsnew-617.tar.gz |
bpo-40334: Add What's New sections for PEP 617 and PEP 585whatsnew-617
-rw-r--r-- | Doc/whatsnew/3.9.rst | 43 |
1 files changed, 43 insertions, 0 deletions
diff --git a/Doc/whatsnew/3.9.rst b/Doc/whatsnew/3.9.rst index 325121df13..728e6001da 100644 --- a/Doc/whatsnew/3.9.rst +++ b/Doc/whatsnew/3.9.rst @@ -115,6 +115,49 @@ to easily remove an unneeded prefix or a suffix from a string. Corresponding added. See :pep:`616` for a full description. (Contributed by Dennis Sweeney in :issue:`18939`.) +PEP 585: Builtin Generic Types +------------------------------ + +In type annotations you can now use built-in collection types such as +``list`` and ``dict`` as generic types instead of importing the +corresponding capitalized types (e.g. ``List`` or ``Dict``) from +``typing``. Some other types in the standard library are also now generic, +for example ``queue.Queue``. + +Example: + +.. code-block:: python + + def greet_all(names: list[str]) -> None: + for name in names: + print("Hello", name) + +See :pep:`585` for more details. (Contributed by Guido van Rossum, +Ethan Smith, and Batuhan Taşkaya in :issue:`39481`.) + +PEP 617: New Parser +------------------- + +Python 3.9 uses a new parser, based on `PEG +<https://en.wikipedia.org/wiki/Parsing_expression_grammar>`_ instead +of `LL(1) <https://en.wikipedia.org/wiki/LL_parser>`_. The new +parser's performance is roughly comparable to that of the old parser, +but the PEG formalism is more flexible than LL(1) when it comes to +designing new language features. We'll start using this flexibility +in Python 3.10 and later. + +The :mod:`ast` module uses the new parser and produces the same AST as +the old parser. + +In Python 3.10, the old parser will be deleted and so will all +functionality that depends on it (primarily the :mod:`parser` module, +which has long been deprecated). In Python 3.9 *only*, you can switch +back to the LL(1) parser using a command line switch (``-X +oldparser``) or an environment variable (``PYTHONOLDPARSER=1``). + +See :pep:`617` for more details. (Contributed by Guido van Rossum, +Pablo Galindo and Lysandros Nikolau in :issue:`40334`.) + Other Language Changes ====================== |