U flag deprecated since Python 3.3 and removed in 3.9

[hugovk]

Fedora bug report: https://bugzilla.redhat.com/show_bug.cgi?id=1792948

python-pylibmc fails to build with Python 3.9.0a2.

+ /usr/bin/python3 setup.py build '--executable=/usr/bin/python3 -s'
Traceback (most recent call last):
  File "/builddir/build/BUILD/pylibmc-1.5.1/setup.py", line 98, in <module>
    with open("README.rst", "U", encoding="utf-8") as r:
ValueError: invalid mode: 'U'

See https://docs.python.org/3.9/whatsnew/3.9.html#changes-in-the-python-api

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. In Python 3, the “universal newline” is used by default when a file is open in text mode. The newline parameter of open() controls how universal newlines works.

Use the default "r" for Python 3.3+.

Python 3.9 is in alpha with a full release due in October.

---

Also, heads up, nose is unmaintained and doesn't work on Python 3.9: nose-devs/nose#1099. You'll need to migrate testing to something new, I'd suggest pytest.

And 3.9-dev is now available on Travis CI.

[hroncok]

Alternatively, you can use io.open() on Python 2 to get a more Python3-like open().

[lericson]

Interesting. I would probably say that the better solution would be to do a major version release, and break with Python 2.x altogether.

[hugovk]

Even better! I'll create a new PR.

[hugovk]

And I'll remove EOL 3.2-3.4 too.

[lericson]

(Also hooray, I outlived nose.)

I think a major version release should include a more thorough cleaning, there is a lot of version testing in the C code.

[hugovk]

Please see PR #258.

[hugovk]

Well this got fixed in 22854a4 so this PR is no longer needed :)

[lericson]

That's right, thanks for noticing!