Bug report

Bug description:

When using anf-string in combination withlambda functions that return non-ASCII characters, either aUnicodeDecodeError or aSystemError is raised, depending on the specific modification made to the code. These errors do not occur consistently, but rather vary based on how the lambdas and string content are altered.

Steps to Reproduce

deftest1(foo,bar):return""deftest2():returnf"{test1(foo=lambda:'、、、、、、、、、、、、、、、、、',bar=lambda:'abcdefghijklmnopqrstuvwxyz 123456789 123456789',    )}"

Run the code withpython <file.py>, which triggers the following error:

UnicodeDecodeError: 'utf-8' codec can't decode bytes in position 28-29: unexpected end of data

Expected Behavior

The code should execute without raising any errors.

Actual Behavior

The following behaviors are observed when making the specified modifications. Each of these cases is independent:

1. Removing one、 character from the first string (foo): No error.
2. Removing all、 characters from the first string:SystemError: Negative size passed to PyUnicode_New.
3. Removingfoo= (i.e., not passingfoo by keyword): No error.
4. Removinglambda: (i.e., makingeither argument orboth into astr type instead of aCallable[[], str]): No error.
5. Removing any character from the second string (bar): No error.

Other Relevant Information

The bug doesnot reproduce in Python 3.13.1, but itdoes reproduce in Python 3.13.2 and 3.12.9.

CPython versions tested on:

3.13

Operating systems tested on:

Linux

Linked PRs

• gh-130618: Fix parser error when using lambdas inside f-strings #130638
• [3.13] gh-130618: Fix parser error when using lambdas inside f-strings (GH-130638) #130642
• [3.12] gh-130618: Fix parser error when using lambdas inside f-strings (GH-130638) #130644