decode the execution path string based file system encoding

[sohero]

When my py file importing matplotlib run in a folder where the path contains gbk encoding character, matplotlib will raise a unicode decode error.The changes in line 666/673/679 will fix the problem.

[tacaswell]

What OS are you on? Can you turn that pattern into a helper function?

attn @mdboom

Checking for the decode attribute and assuming that it is encoded and making assumptions about what that encoding is seems sketchy to me, is there a better way to do this?

[mdboom]

The issue here is that we take the a path we get from Python and get a byte string back. Using that byte string to open the file again would be totally fine and correct. The problem is that we tack other things onto that path using a unicode string -- os.sep.join([__file__, u'mpl-data']) -- which forces the path to be decoded from a byte string into unicode using the default encoding, which, on @sohero's system, I'll assume is different from the file system encoding. Python can't really do better since it doesn't know the path is a filesystem path and not some random string. (FWIW, os.path.join has the same issue, though I'd assume it could do better). You could, alternatively, encode the bit we are adding into the file system encoding before joining, and keep everything as byte strings, but that's not really an improvement.

So, I think what this PR is doing is fine in general. However, I agree there should be a helper function for this, maybe decode_filesystem_path(). And I don't think we should do hasattr(obj, 'decode'), though. Maybe isinstance(obj, bytes) instead.

[sohero]

My working OS is windows 7 Chinese version, the default file system encoding is gbk. Python 2.X can not detect the encoding correctly, and Matplotlib works well when the path only contains english chars, while not working when the path has any non-ascii chars like 中文. Using a helper function isinstance(obj, bytes) make the codes more readable and reliable. Thanks for the reminder.

[tacaswell]

@sohero Thank you! I believe this is your first mpl contribution, congratulations.