bpo-37330: open() no longer accept 'U' in file mode

[vstinner]

open(), io.open(), codecs.open() and fileinput.FileInput no longer
accept "U" ("universal newline") in the file mode. This flag was
deprecated since Python 3.3.

https://bugs.python.org/issue37330

[serhiy-storchaka]

Needed changes in imp.py and fileinput.py.

[bedevere-bot]

When you're done making the requested changes, leave the comment: I have made the requested changes; please review again.

[tirkarthi]

imp.py also does a similar check for U to be valid in

cpython/Lib/imp.py

Line 228 in 5954334

ifmodeand (notmode.startswith(('r', 'U')) or'+'inmode):

but the module is deprecated and it would fail at open with similar ValueError that "U" is invalid so not sure if it needs to be changed.

Edit: Saw Serhiy's review about imp.py just after refresh.

[vstinner]

@tirkarthi@serhiy-storchaka: I made requested changes.

[vstinner]

Oh, the Doc job of Travis CI fails with:

Sphinx parallel build error:
ValueError: invalid mode: 'rU'

Sphinx still uses rU mode.

[vstinner]

Sphinx issue comes from docutils:

 Exception occurred:
File "/home/vstinner/prog/python/master/Doc/venv/lib/python3.9/site-packages/docutils/io.py", line 245, in __init__
self.source = open(source_path, mode, **kwargs)
ValueError: invalid mode: 'rU'

Extract of the code, it seems to contain a copy of fileinput.FileInput:

class FileInput(Input):
def __init__(self, source=None, source_path=None,
encoding=None, error_handler='strict',
autoclose=True, mode='rU', **kwargs):
...
if source is None:
if source_path:
...
try:
self.source = open(source_path, mode, **kwargs)
except IOError as error:
raise InputError(error.errno, error.strerror, source_path)

[vstinner]

I reported the docutils issue to docutils bug tracker with a patch: https://sourceforge.net/p/docutils/bugs/363/

[vstinner]

This PR cannot be merged because it breaks the Python CI because of docutils: https://bugs.python.org/issue37330#msg346219

I prefer to close this PR right now. I will not be available next weeks, so I prefer to close the PR. I may reopen it later, once docutils is fixed.

[tirkarthi]

@vstinner docutils 0.15 was released on July 21 which has the patch for 'U' mode. The current build config uses docutils>=0.12 in requirements so docutils 0.15 is used in the builds which and hence should be fix the issue.

[vstinner]

@vstinner docutils 0.15 was released on July 21 which has the patch for 'U' mode. The current build config uses docutils>=0.12 in requirements so docutils 0.15 is used in the builds which and hence should be fix the issue.

Nice. I tried to reopen the issue after I rebased my branch, but I made a mistake and I'm no longer able to open the PR. So I created PR #16959 instead.