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gh-102856: Add changes related to PEP 701 in 3.12 What's New docs (#104824)
Co-authored-by: Pablo Galindo Salgado <Pablogsal@gmail.com> Co-authored-by: Jelle Zijlstra <jelle.zijlstra@gmail.com>
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Marta Gómez Macías
GitHub
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1 changed files with 135 additions and 16 deletions
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@ -66,6 +66,10 @@ Summary -- Release highlights
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.. PEP-sized items next.
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New grammar features:
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* :pep:`701`: Syntactic formalization of f-strings
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New typing features:
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* :pep:`688`: Making the buffer protocol accessible in Python
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@ -136,22 +140,70 @@ Improved Error Messages
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New Features
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============
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* Add :ref:`perf_profiling` through the new
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environment variable :envvar:`PYTHONPERFSUPPORT`,
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the new command-line option :option:`-X perf <-X>`,
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as well as the new :func:`sys.activate_stack_trampoline`,
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:func:`sys.deactivate_stack_trampoline`,
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and :func:`sys.is_stack_trampoline_active` APIs.
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(Design by Pablo Galindo. Contributed by Pablo Galindo and Christian Heimes
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with contributions from Gregory P. Smith [Google] and Mark Shannon
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in :gh:`96123`.)
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* The extraction methods in :mod:`tarfile`, and :func:`shutil.unpack_archive`,
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have a new a *filter* argument that allows limiting tar features than may be
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surprising or dangerous, such as creating files outside the destination
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directory.
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See :ref:`tarfile-extraction-filter` for details.
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In Python 3.14, the default will switch to ``'data'``.
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(Contributed by Petr Viktorin in :pep:`706`.)
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.. _whatsnew312-pep701:
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PEP 701: Syntactic formalization of f-strings
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---------------------------------------------
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:pep:`701` lifts some restrictions on the usage of f-strings. Expression components
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inside f-strings can now be any valid Python expression including backslashes,
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unicode escaped sequences, multi-line expressions, comments and strings reusing the
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same quote as the containing f-string. Let's cover these in detail:
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* Quote reuse: in Python 3.11, reusing the same quotes as the containing f-string
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raises a :exc:`SyntaxError`, forcing the user to either use other available
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quotes (like using double quotes or triple quotes if the f-string uses single
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quotes). In Python 3.12, you can now do things like this:
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>>> songs = ['Take me back to Eden', 'Alkaline', 'Ascensionism']
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>>> f"This is the playlist: {", ".join(songs)}"
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'This is the playlist: Take me back to Eden, Alkaline, Ascensionism
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Note that before this change there was no explicit limit in how f-strings can
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be nested, but the fact that string quotes cannot be reused inside the
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expression component of f-strings made it impossible to nest f-strings
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arbitrarily. In fact, this is the most nested f-string that could be written:
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>>> f"""{f'''{f'{f"{1+1}"}'}'''}"""
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'2'
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As now f-strings can contain any valid Python expression inside expression
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components, it is now possible to nest f-strings arbitrarily:
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>>> f"{f"{f"{f"{f"{f"{1+1}"}"}"}"}"}"
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'2'
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* Multi-line expressions and comments: In Python 3.11, f-strings expressions
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must be defined in a single line even if outside f-strings expressions could
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span multiple lines (like literal lists being defined over multiple lines),
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making them harder to read. In Python 3.12 you can now define expressions
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spaning multiple lines and include comments on them:
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>>> f"This is the playlist: {", ".join([
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... 'Take me back to Eden', # My, my, those eyes like fire
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... 'Alkaline', # Not acid nor alkaline
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... 'Ascensionism' # Take to the broken skies at last
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... ])}"
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'This is the playlist: Take me back to Eden, Alkaline, Ascensionism'
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* Backslashes and unicode characters: before Python 3.12 f-string expressions
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couldn't contain any ``\`` character. This also affected unicode escaped
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sequences (such as ``\N{snowman}``) as these contain the ``\N`` part that
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previously could not be part of expression components of f-strings. Now, you
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can define expressions like this:
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>>> print(f"This is the playlist: {"\n".join(songs)}")
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This is the playlist: Take me back to Eden
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Alkaline
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Ascensionism
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>>> print(f"This is the playlist: {"\N{BLACK HEART SUIT}".join(songs)}")
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This is the playlist: Take me back to Eden♥Alkaline♥Ascensionism
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See :pep:`701` for more details.
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(Contributed by Pablo Galindo, Batuhan Taskaya, Lysandros Nikolaou, Cristián
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Maureira-Fredes and Marta Gómez in :gh:`102856`. PEP written by Pablo Galindo,
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Batuhan Taskaya, Lysandros Nikolaou and Marta Gómez).
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.. _whatsnew312-pep709:
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@ -223,6 +275,24 @@ See :pep:`692` for more details.
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Other Language Changes
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======================
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* Add :ref:`perf_profiling` through the new
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environment variable :envvar:`PYTHONPERFSUPPORT`,
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the new command-line option :option:`-X perf <-X>`,
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as well as the new :func:`sys.activate_stack_trampoline`,
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:func:`sys.deactivate_stack_trampoline`,
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and :func:`sys.is_stack_trampoline_active` APIs.
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(Design by Pablo Galindo. Contributed by Pablo Galindo and Christian Heimes
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with contributions from Gregory P. Smith [Google] and Mark Shannon
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in :gh:`96123`.)
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* The extraction methods in :mod:`tarfile`, and :func:`shutil.unpack_archive`,
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have a new a *filter* argument that allows limiting tar features than may be
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surprising or dangerous, such as creating files outside the destination
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directory.
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See :ref:`tarfile-extraction-filter` for details.
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In Python 3.14, the default will switch to ``'data'``.
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(Contributed by Petr Viktorin in :pep:`706`.)
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* :class:`types.MappingProxyType` instances are now hashable if the underlying
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mapping is hashable.
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(Contributed by Serhiy Storchaka in :gh:`87995`.)
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@ -543,6 +613,14 @@ tkinter
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like ``create_*()`` methods.
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(Contributed by Serhiy Storchaka in :gh:`94473`.)
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tokenize
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--------
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* The :mod:`tokenize` module includes the changes introduced in :pep:`701`. (
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Contributed by Marta Gómez Macías and Pablo Galindo in :gh:`102856`.)
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See :ref:`whatsnew312-porting-to-python312` for more information on the
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changes to the :mod:`tokenize` module.
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types
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-----
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@ -687,6 +765,11 @@ Optimizations
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* Speed up :class:`asyncio.Task` creation by deferring expensive string formatting.
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(Contributed by Itamar O in :gh:`103793`.)
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* The :func:`tokenize.tokenize` and :func:`tokenize.generate_tokens` functions are
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up to 64% faster as a side effect of the changes required to cover :pep:`701` in
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the :mod:`tokenize` module. (Contributed by Marta Gómez Macías and Pablo Galindo
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in :gh:`102856`.)
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CPython bytecode changes
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========================
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@ -1130,6 +1213,8 @@ Removed
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Iceape, Firebird, and Firefox versions 35 and below (:gh:`102871`).
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.. _whatsnew312-porting-to-python312:
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Porting to Python 3.12
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======================
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@ -1201,6 +1286,40 @@ Changes in the Python API
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that may be surprising or dangerous.
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See :ref:`tarfile-extraction-filter` for details.
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* The output of the :func:`tokenize.tokenize` and :func:`tokenize.generate_tokens`
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functions is now changed due to the changes introduced in :pep:`701`. This
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means that ``STRING`` tokens are not emitted any more for f-strings and the
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tokens described in :pep:`701` are now produced instead: ``FSTRING_START``,
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``FSRING_MIDDLE`` and ``FSTRING_END`` are now emitted for f-string "string"
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parts in addition to the appropriate tokens for the tokenization in the
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expression components. For example for the f-string ``f"start {1+1} end"``
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the old version of the tokenizer emitted::
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1,0-1,18: STRING 'f"start {1+1} end"'
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while the new version emits::
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1,0-1,2: FSTRING_START 'f"'
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1,2-1,8: FSTRING_MIDDLE 'start '
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1,8-1,9: OP '{'
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1,9-1,10: NUMBER '1'
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1,10-1,11: OP '+'
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1,11-1,12: NUMBER '1'
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1,12-1,13: OP '}'
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1,13-1,17: FSTRING_MIDDLE ' end'
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1,17-1,18: FSTRING_END '"'
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Aditionally, there may be some minor behavioral changes as a consecuence of the
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changes required to support :pep:`701`. Some of these changes include:
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* Some final ``DEDENT`` tokens are now emitted within the bounds of the
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input. This means that for a file containing 3 lines, the old version of the
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tokenizer returned a ``DEDENT`` token in line 4 whilst the new version returns
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the token in line 3.
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* The ``type`` attribute of the tokens emitted when tokenizing some invalid Python
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characters such as ``!`` has changed from ``ERRORTOKEN`` to ``OP``.
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Build Changes
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=============
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