Py3 compat

[danielballan]

• Use six. (For the uninitiated, it's a package commonly used to simplify py2/3 compatibility.)
• Remove py2-isms (print statements, has_key, etc.)
• Remove homebrewed versioning code in favor of versioneer.
• Remove a couple unused imports.

The important module is importable in Python 3:

In [1]: import diffpy.srxplanar
Only tiff or .npy mask is support since fabio is not available

and versioneer is doing its job.

In [2]: import diffpy

In [3]: diffpy.__version__
Out[3]: '1.1+39.g3a19323.dirty'

The +39 means 39 commits past version 1.1, and the .dirty means there was uncommitted code when I ran this. The last commit was hash g3a19323....

I followed the existing convention of exposing __version__ in the subpackages, although this is a little unusual. You can see that they all still work.

In [4]: diffpy.srxplanar.__version__
Out[4]: '1.1+39.g3a19323.dirty'

In [5]: diffpy.confutils.__version__
Out[5]: '1.1+39.g3a19323.dirty'

attn @pavoljuhas

[zthatch]

@danielballan thank you for already having done what I was recently assigned. Looks like I will just add test code to prove that this works on python 2 and 3 (specifically testing how it interfaces with srxplanargui and pdfgetxgui).

It also looks like there is now a conflict, so I will see if I can pull your PR and rebase.

I still have to have a conversation with @pavoljuhas about versioning and will likely switch from versioneer to Rever.

[pavoljuhas]

diffpy is a namespace-only (for Python-import) package to mark up software packages / products belonging to the DiffPy suite. There are diffpy.structure, diffpy.pdfgui, diffpy.srreal, etc., on PyPI and Conda repositories; each of them installs a diffpy namespace in a way that other diffpy.SOMETHING subpackages are visible and importable even if they reside in a different PYTHONPATH directory.

I'd advice against putting version value or any other content (except of namespacing support) to diffpy/__init__.py, because it would cause conflicts and unpredictable results when several diffpy.SOMETHING packages were installed.