Python 3.13.0b1: exec() does not populate locals()

Bug report

Bug description:

x.py

xxx = 118888

readx.py

def f():
    with open("x.py", encoding="utf-8") as f:
        exec(compile(f.read(), "x.py", "exec"))
    return locals()["xxx"]

print(f())

shell

$ python3.12 readx.py
118888

$ python3.13 readx.py
Traceback (most recent call last):
  File ".../readx.py", line 6, in <module>
    print(f())
          ~^^
  File ".../readx.py", line 4, in f
    return locals()["xxx"]
           ~~~~~~~~^^^^^^^
KeyError: 'xxx'

This breaks e.g. pillow 10.3.0 which has:

def get_version():
    version_file = "src/PIL/_version.py"
    with open(version_file, encoding="utf-8") as f:
        exec(compile(f.read(), version_file, "exec"))
    return locals()["__version__"]

In https://github.com/python-pillow/Pillow/blob/10.3.0/setup.py#L23

CPython versions tested on:

3.13

Operating systems tested on:

Linux

Linked PRs

Current plan for changes

Add this paragraph to the main PEP 667 description in the 3.13 "What's New?" doc:

The change to the semantics of locals() in optimized scopes also affects the default behaviour of code execution functions that implicitly target locals() if no explicit namespace is provided (such as exec and eval). In previous versions, whether or not the changes could be accessed by calling locals() after the code finished execution was implementation dependent. In CPython specifically, such code would often appear to work as desired, but could sometimes fail in optimized scopes based on other code (including debuggers and code execution tracing tools) potentially resetting the shared snapshot in that scope. Now, the code will always run against an independent snapshot of locals() in optimized scopes, and hence the changes will never be visible in subsequent calls to locals(). To access the changes made in these cases, an explicit namespace reference must now be passed to the relevant function. Alternatively, it may make sense to switch over to using a higher level code execution API that returns the resulting code execution namespace (such as runpy.run_path).

Add this sentence to the porting note:

Code execution functions that implicitly target locals() (such as exec and eval) must be passed an explicit namespace to access their results in an optimized scope.

No PR yet as I'll merge #119379 before making any further PEP 667 related updates.

gh-118888: Further PEP 667 docs updates (gh-119893)

pythongh-118888: Further PEP 667 docs updates (pythongh-119893)

[3.13] gh-118888: Further PEP 667 docs updates (gh-119894)

pythongh-118888: Further PEP 667 docs updates (pythongh-119893)

setup.py: Fix version retrieval on Python 3.13+

Update `setup.py` to accommodate `Python3.13.0`

py-Pillow: add py313 subport

Fix get_version for Python 3.13

Fixes __version__ not found error with Python 3.13 (see python/cpytho…

fix locals() writable, does not seem to work on py313

Fixes __version__ not found error with Python 3.13 (see python/cpytho…

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Python 3.13.0b1: exec() does not populate locals() #118888

Bug report

Bug description:

x.py

readx.py

shell

CPython versions tested on:

Operating systems tested on:

Linked PRs

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Python 3.13.0b1: exec() does not populate locals() #118888

Description

Bug report

Bug description:

x.py

readx.py

shell

CPython versions tested on:

Operating systems tested on:

Linked PRs

Activity

ncoghlan commented on May 30, 2024

ncoghlan commented on May 31, 2024

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