Merge {IO,Environment,Windows}Error into OSError for Python 3.3+

[intgr]

Starting with Python 3.3, IOError, EnvironmentError and WindowsError are
aliases for OSError, which has all their attributes.

Also, tested on Python 3.6 that OSError.filename/filename2 may also be
bytes and None, so annotated them as Any.

Reference:

• https://docs.python.org/3/library/exceptions.html#OSError
• https://www.python.org/dev/peps/pep-3151/

[intgr]

Is it a good idea to put sys.platform checks in? The winerror attribute is missing entirely on non-Windows platforms.

[JelleZijlstra]

Yes, that makes sense.

[srittau]

Question for the maintainers: Can't we leave out the branch for Python < 3.3? README.md says that typeshed targets Python 2.7 and 3.3+.

[JelleZijlstra]

Yes, we don't care about 3.0-3.2. (We could also seriously consider dropping support for 3.3, since that has reached EOL.)

[intgr]

Thanks! I got rid of the Python <3.3 check.

It still fails a test in mypy code, which uses OSError.filename. The filename is being assigned to a variable that was inferred to str but fails since the attribute is now labelled Union[str, bytes, None]. See https://github.com/python/mypy/blob/master/mypy/test/data.py#L318-L323

What's the correct fix in this case? Should I submit a PR to mypy to create a new variable in this context? Or should I revert the filename type annotation back to str? Or are there some other options?

[intgr]

I created a PR for Mypy here: python/mypy#4541. I'll see whether that gets merged.

[intgr]

Per comment from GvR, I changed the filename/filename2 type to Any instead of Union to avoid this issue. All tests pass now.

[ambv]

Thanks! ✨ 🍰 ✨