Deprecate Python 2.7

[noviluni]

As part of the next version 1.0.0 we will deprecate Python 2.7. I have just created this ticket to track it.

• Merge as more finished PRs as possible (to avoid future file conflicts)
• Change tox and Travis to test only with Python 3. (ref: Remove pypy and python2 from tox and travis. #744)
• Change the setup file. (ref: Change setup.py #755)
• Apply 2to3 and review carefully (__future__ imports, unicode strings...) (ref: Apply 2to3 to clean code #748)
• Remove six package (ref: Remove usage of six package. #754)
• Remove utf declaration strings (ref: Remove utf declaration strings. #758, Update write_complete_data script to remove utf encoding string. #761, Remove encoding from ordering languages script #764)
• Check specific code for Python 2 that can be removed or refactored (remove object and change super() syntax #763, remove some python2 specific code #749, Remove python2 reminiscenses #777)
• Check and update docs and comments (remove python2/unicode references #783)

[kishan3]

Hi @noviluni Is it possible to list tasks we need to do perform deprecation?
Or we just need to check it file by file?

[noviluni]

Hi @kishan3, we have some pending PRs labeled as breaking-change ( breaking-change ) that I'm waiting to merge after seeing that this last release is stable enough. If we don't see any major issue raised before the 15th of July, we will merge those PRs and after that starting to migrate the library to Python 3 code (deprecating Python 2.7).

My idea is to:

• Merge as more finished PRs as possible (to avoid future file conflicts)
• Change tox and Travis to test only with Python 3.
• Change the setup file.
• Proceed with code changes.

From my experience, the best way to proceed is by using the 2to3 library (reviewing manually each change as some things are not always necessary). After that, we will remove the six package, remove the utf declaration strings and check if there are specific code for Python 2 or Python 3 that can be removed or refactored.

To avoid really big PRs, I think that we could start by using 2to3 in some specific sections (for example in tests, in scripts, etc.).

[noviluni]

Today is the 15th and no big issues have been raised so far, so we can start deprecating Python 2! 💪

I finished merging some PRs with breaking changes that were waiting. Now we can proceed with deleting the Python 2 and PyPI environments from tox and Travis.