"U" mode is no longer accepted from Python 3.9

[tirkarthi]

PyDev.Debugger/_pydev_imps/_pydev_pkgutil_old.py
261:                self.file = open(self.filename, 'rU')
306:                    f = open(self.filename[:-1], 'rU')

PyDev.Debugger/_pydev_runfiles/pydev_runfiles.py
212:                f = open(config_file, 'rU')

PyDev.Debugger/third_party/pep8/pycodestyle.py
1326:        with open(filename, 'rU') as f:

PyDev.Debugger/third_party/isort_container/isort/settings.py
217:    with open(file_path, 'rU') as config_file:

https://github.com/python/cpython/pull/16959

[fabioz]

Thanks for the report... it seems the change was reverted (https://github.com/python/cpython/pull/18767), so, at least for 3.9 it will still be accepted (so, there's until 3.10 to fix it).

We should probably run test checking for deprecation issues to avoid such things in the future (https://docs.python.org/dev/whatsnew/3.9.html#you-should-check-for-deprecationwarning-in-your-code).

[juliangilbey]

That shouldn't be an issue as _pydev_imps/_pydev_pkgutil_old.py is only imported if not IS_PY3K, so Python 3.9 and above will never see this Python 2.x code.