avoid a warning by PyTypeChecker

[foreverseer]

NDFrame.to_csv(str) got a warning by PyTypeChecker, "Expected type 'None', got 'str' instead"
use typing.Union to combine type "FilePathOrBuffer[AnyStr]" and "None", instead of " | " can avoid it.

• closes #xxxx
• tests added / passed
• Ensure all linting tests pass, see here for how to run them
• whatsnew entry

[pep8speaks]

Hello @foreverseer! Thanks for updating this PR. We checked the lines you've touched for PEP 8 issues, and found:

There are currently no PEP 8 issues detected in this Pull Request. Cheers! 🍻

Comment last updated at 2021-11-16 01:40:18 UTC

[twoertwein]

If PyTypeChecker cannot handle |, then it might be worth to open a bug at PyTypeChecker? Pandas is not yet a py.typed library, can you double-check that PyTypeChecker is getting the type annotations from pandas (or a third-party stub file)?

Do you mind testing whether PyTypeChecker still has the issue on master? You are welcome to also test PyTypeChecker with #43951.

[foreverseer]

If PyTypeChecker cannot handle |, then it might be worth to open a bug at PyTypeChecker? Pandas is not yet a py.typed library, can you double-check that PyTypeChecker is getting the type annotations from pandas (or a third-party stub file)?

Do you mind testing whether PyTypeChecker still has the issue on master? You are welcome to also test PyTypeChecker with #43951.

pytypechecker is a function of pycharm
i mean not use Union to combine two type will cause a warning of pycharm

↑this is pycharm's warning

[twoertwein]

pandas/core/generic.py uses the python 3.10+ syntax | (equivalent to typing.Union) and also has from __future__ import annotations which enables this syntax for older versions of python.

I recomend opening a bug with pycharm (after checking that pycharm is using the tpye annotations shipped with pandas itself - most likely it uses 3rd-party type stubs).

[mroeschke]

Agreed, pandas uses | instead of Union consistently in the code base so it appears that this is more of an upstream issue. Closing.