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gh-148641: Flesh out PEP 829 for What's New #149347

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hugovk merged 7 commits into from
May 6, 2026
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gh-148641: Flesh out PEP 829 for What's New #149347

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5fb40ee
Flesh out PEP 829 for What's New
warsaw May 4, 2026
82a0cdf
Merge branch 'main' into warsaw/829-followup
warsaw May 4, 2026
0d1070b
Update Doc/whatsnew/3.15.rst
warsaw May 4, 2026
d330ef4
Update Doc/whatsnew/3.15.rst
warsaw May 4, 2026
32c9865
Move PEP 829 before the typing PEPs block
hugovk May 6, 2026
64a475c
Merge remote-tracking branch 'upstream/main' into warsaw/829-followup
hugovk May 6, 2026
e372f81
Link to .pth and .start files docs
hugovk May 6, 2026
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27 changes: 26 additions & 1 deletion Doc/whatsnew/3.15.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -81,6 +81,7 @@ Summary -- Release highlights
<whatsnew315-unpacking-in-comprehensions>`
* :pep:`686`: :ref:`Python now uses UTF-8 as the default encoding
<whatsnew315-utf8-default>`
* :pep:`829`: :ref:`Package startup configuration files <whatsnew315-startup-files>`
* :pep:`728`: :ref:`TypedDict with typed extra items <whatsnew315-typeddict>`
* :pep:`747`: :ref:`Annotating type forms with TypeForm
<whatsnew315-typeform>`
Expand All @@ -94,7 +95,6 @@ Summary -- Release highlights
* :ref:`Improved error messages <whatsnew315-improved-error-messages>`
* :ref:`The official Windows 64-bit binaries now use the tail-calling interpreter
<whatsnew315-windows-tail-calling-interpreter>`
* :pep:`829`: Package Startup Configuration Files

New features
============
Expand Down Expand Up @@ -452,6 +452,31 @@ agen() for x in a)``.

(Contributed by Adam Hartz in :gh:`143055`.)

.. _whatsnew315-startup-files:

:pep:`829`: Package startup configuration files
-----------------------------------------------

Loaded by the :mod:`site` module when ``-S`` is not given, :ref:`.pth files <site-pth-files>`
can contain lines that both extend :data:`sys.path` and execute arbitrary code
when the line starts with ``import`` (followed by a space or tab). The latter
functionality can be problematic, since it is difficult to know exactly what
gets executed when Python starts up.

As a step towards improving the ability to audit pre-start executable code,
Python 3.15 introduces :ref:`.start files <site-start-files>` which contain entry point
specifications of the form ``pkg.mod:callable`` where ``pkg.mod`` is the
import path to the given callable. When Python starts up, the callable is
located and called with no arguments.

``import`` lines in :file:`.pth` files are silently deprecated. When a
matching :file:`.start` file is found, ``import`` lines in :file:`.pth` files
are ignored. There is no change to :data:`sys.path` extension lines in
:file:`.pth` files.

(Contributed by Barry Warsaw in :gh:`148641`.)


.. _whatsnew315-abi3t:

:pep:`803` -- Stable ABI for Free-Threaded Builds
Expand Down
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