Crash report

What happened?

from concurrent.futures import InterpreterPoolExecutor


executor = InterpreterPoolExecutor()


def f():
    import _datetime
    print(_datetime)


executor.submit(f)
executor.submit(f)

executor.shutdown()

This code may lead to a interpreter crash:

PS C:\Users\xxx\Source\cpython> .\python.bat .\a.py
Running Debug|x64 interpreter...
<module '_datetime' (built-in)>  # The first sub-interpreter's output
Assertion failed: !managed_static_type_index_is_set(self), file C:\Users\xxxxx\Source\cpython\Objects\typeobject.c, line 317

Please note that there is a similar issue may crash the interpreter but in the sestructing phase: #136423

My analyze

The _datetime module will call _PyStaticType_InitForExtension to initialize some static types. Look at it's implementation:

It's using tp_flags Py_TPFLAGS_READY to determine if this type is already initialized. And at last it will call managed_static_type_state_init with the initialized flag.

If the type flag Py_TPFLAGS_READY was not set before, and another sub-interpreter has been initialized, finished, and has set the Py_TPFLAGS_READY flag, this assertion will be triggered:

CPython versions tested on:

CPython main branch

Operating systems tested on:

macOS, Windows

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

Python 3.15.0a0 (heads/main:ba9c1986305, Jul 8 2025, 22:13:18) [MSC v.1943 64 bit (AMD64)]

Linked PRs

• gh-136421: Fix crash when _datetime is been initialized in multiple sub-interpreters #136422
• gh-136421: Load _datetime static types during interpreter initialization #136583
• gh-136421: Fix crash in _datetime when initialized/finalized concurrently #136620
• [3.14] gh-136421: Load _datetime static types during interpreter initialization (GH-136583) #136943