Incorrect argument type for `str()` crashes the interpreter

[pschanely]

Crash report

What happened?

Using a byte string for the encoding parameter of str() results in a crash (instead of the expected TypeError):

str(b"hello", b"ascii")

Here is the output I get on macos, 3.13.0b4:

% python
Python 3.13.0b4 (main, Jul 24 2024, 12:21:52) [Clang 15.0.0 (clang-1500.3.9.4)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> str(b"hello", b"ascii")
Fatal Python error: _Py_CheckFunctionResult: a function returned a result with an exception set
Python runtime state: initialized
TypeError: str() argument 'encoding' must be str, not bytes

The above exception was the direct cause of the following exception:

SystemError: <class 'str'> returned a result with an exception set

Current thread 0x00000002064b0c00 (most recent call first):
  File "<python-input-0>", line 1 in <module>
  File "/Users/phillipschanely/.pyenv/versions/3.13.0b4-debug/lib/python3.13/code.py", line 91 in runcode
  File "/Users/phillipschanely/.pyenv/versions/3.13.0b4-debug/lib/python3.13/_pyrepl/console.py", line 200 in runsource
  File "/Users/phillipschanely/.pyenv/versions/3.13.0b4-debug/lib/python3.13/code.py", line 303 in push
  File "/Users/phillipschanely/.pyenv/versions/3.13.0b4-debug/lib/python3.13/_pyrepl/simple_interact.py", line 156 in run_multiline_interactive_console
  File "/Users/phillipschanely/.pyenv/versions/3.13.0b4-debug/lib/python3.13/_pyrepl/main.py", line 57 in interactive_console
  File "/Users/phillipschanely/.pyenv/versions/3.13.0b4-debug/lib/python3.13/_pyrepl/__main__.py", line 6 in <module>
  File "/Users/phillipschanely/.pyenv/versions/3.13.0b4-debug/lib/python3.13/runpy.py", line 88 in _run_code
  File "/Users/phillipschanely/.pyenv/versions/3.13.0b4-debug/lib/python3.13/runpy.py", line 198 in _run_module_as_main
zsh: abort      python

CPython versions tested on:

CPython main branch

Operating systems tested on:

macOS

Output from running 'python -VV' on the command line:

Python 3.13.0b4 (main, Jul 24 2024, 12:21:52) [Clang 15.0.0 (clang-1500.3.9.4)]

Linked PRs

• gh-122888: Fix crash on certain calls to str() #122889
• [3.13] gh-122888: Fix crash on certain calls to str() (GH-122889) #122947

[ZeroIntensity]

Note that the crash only occurs on debug builds.

[JelleZijlstra]

Thanks, I submitted a fix. The issue goes back to at least 3.13.0b2 but I didn't look for the exact culprit.

On release builds it throws a SystemError instead. When pure Python code raises SystemError it is almost always a bug.

[JelleZijlstra]

Marking as a release blocker to make sure this gets merged before the next 3.13 RC.