argparse: Check if stderr is defined before writing to it

[simaoafonso-pwt]

Bug report

argparse tries to write to stderr inconditionally, even when it's None. This is only a problem on Windows. Here:

https://github.com/python/cpython/blob/3.11/Lib/argparse.py#L2596-L2600

I detected this when using PyInstaller to create a binary on Windows using --noconsole, which triggers using pythonw.exe. In this case, sys.stderr is None.

This is similar to #89057

Your environment

• Any version of Python on Windows, up to 3.11

Linked PRs

• gh-101640: Make argparse working in pythonw by dropping stderr writes there #101802
• [3.11] gh-101640: Make argparse _print_message catch any write error (GH-101802) #104250