bpo-43510: Remove _pyio.OpenWrapper class

[methane]

https://bugs.python.org/issue43510

[eryksun]

Are you checking this here instead of leaving it up to the open call in order to raise the warning at the right stack level?

[methane]

Yes. text_encoding() is used for it.

[eryksun]

Okay, so this is just a particular problem in an unusual case of a proxy call that needs to bring the text_encoding call forward, with special handling such as checking if "b" not in mode.

[vstinner]

OpenWrapper is really a weird beast. I don't know other functions which are defined this way. Can't we decorate def open with @staticmethod instead?

The io module doesn't use this hack: OpenWrapper is just an alias to open.

$ python3
Python 3.9.2 (default, Feb 20 2021, 00:00:00) 
>>> import io
>>> io.OpenWrapper
<built-in function open>
>>> io.OpenWrapper is io.open
True

[methane]

OpenWrapper is really a weird beast. I don't know other functions which are defined this way. Can't we decorate def open with @staticmethod instead?

Nice idea.

[methane]

Oh, test is failing...

======================================================================
ERROR: test_read (test.test_univnewlines.PyTestCRLFNewlines)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/runner/work/cpython/cpython/Lib/test/test_univnewlines.py", line 51, in setUp
    with self.open(os_helper.TESTFN, self.WRITEMODE) as fp:
TypeError: 'staticmethod' object is not callable

[vstinner]

I opened a discussion on python-dev about OpenWrapper and staticmethod: https://mail.python.org/archives/list/[email protected]/thread/QZ7SFW3IW3S2C5RMRJZOOUFSHHUINNME/

[vstinner]

I opened a discussion on python-dev about OpenWrapper and staticmethod: https://mail.python.org/archives/list/[email protected]/thread/QZ7SFW3IW3S2C5RMRJZOOUFSHHUINNME/

And I created https://bugs.python.org/issue43680 to remove undocumented io.OpenWrapper and _pyio.OpenWrapper.

[eryksun]

Maybe define open as a classmethod in a dummy class and set the bound method as global open. Or continue to define open as a function, and set OpenWrapper as a functools.partial instance, since it's builtin and doesn't insert a stack frame.