Fix for python3 issues

[thoas]

• Add a compat layer for missing methods or moved methods (based on six)
• Fix bytes issues when using crc32
• Some flake8 issues

Available if you want more information.

[mattrobenolt]

@thoas looks like all of the python 3 tests fail because our dependencies aren't python 3 compatible. :(

[thoas]

@mattrobenolt yep, it seems pycassa is not compatible at all with python3 : even the current master doesn't pass at all.

Do you have a recommendation for this case? I think we need to disable pycassa tests for py3.

[mattrobenolt]

I'm not sure off the top of my head. I think that's reasonable though if that's the only incompatibility.

tbh though, I'd like to rip out pycassa support since that's silly in nydus. :) Not sure why it was a thing in the first place.

[mattrobenolt]

Also, pycassa is deprecated in favor of https://github.com/datastax/python-driver, so I'd be open to ripping that out if we get full python 3 compat without it.

[thoas]

@mattrobenolt I have disabled pycassa tests in Python 3 context.
I think, it would be better to remove the support in another PR.

I need your brain on a nasty choice in Python 3, mine is melting.

======================================================================
ERROR: test_nonzero (tests.nydus.db.connections.tests.EventualCommandTest)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Users/thoas/Sites/Python/ulule/nydus/tests/nydus/db/connections/tests.py", line 354, in test_nonzero
    self.assertEqual(int(ec or 0), 0)
  File "/Users/thoas/Sites/Python/ulule/nydus/nydus/db/promise.py", line 140, in __len__
    return len(self.__wrapped)
TypeError: object of type 'NoneType' has no len()

I lost the self when resolving a promise to None which is ok since it's the exact behavior on Python 2, but ec or 0 in Python 3 is stricter and raises an exception instead of keeping the 0 default value.

What do you suggest for these case scenario?

[thoas]

@mattrobenolt 🎉 🎉 tests are passing on py2/py3

Give me your feedback when you will have the time :)

[thoas]

@mattrobenolt any time on your side to review this PR?

Thanks :)

[mattrobenolt]

This mostly seems ok to me.

/cc @dcramer opinions?

[dcramer]

idc you guys are in charge :)

[mattrobenolt]

[mattrobenolt]

I'm going to review this and compare with my progress that I made on my py3 branch from a while ago that I didn't finish.

master...py3 for reference.

[thoas]

We are in charge 😱 😱

[thoas]

@mattrobenolt any feedback on this?

Thank you :)