Use enum34 when running tests on pre-3.4 Python versions

[JukkaL]

Currently enum is treated Python 3.4 only.

[berdario]

If I understand this correctly, this also means that the stub won't be used in Python3.5

[o11c]

@berdario the internal logic, just checks whether the name is enum.Enum, so if the stub is found it will work. Might also want to change the testsuite bits though.

[berdario]

I see. I'm not sure if the stub is correctly found then.

I wrote a small project to try out mypy, now that typing is in the stdlib, and I had to add a couple of ugly Any type declarations to get it to type check:

https://github.com/berdario/resumable-urlretrieve/blob/faa631f/resumable/__init__.py#L28-L29

Aside from that, it works quite well, and I even got travis-ci to run mypyat every commit to type check the module :D

[o11c]

I don't think mypy is fully compatible with the stdlib's typing yet, I haven't been following that closely though.

[JelleZijlstra]

I think this is a typeshed issue now, but we still need enum34 stubs in typeshed.

[JukkaL]

Apparently enum34 just installs enum, so making the current typeshed stubs available for all Python versions might be good enough. However, this issue is no longer relevant since we no longer use typeshed stubs for enum in mypy tests.