COMPAT: Import abstract classes from collections.abc

[holymonson]

Changed in version 3.3: Moved Collections Abstract Base Classes to the collections.abc module. For backwards compatibility, they continue to be visible in this module through Python 3.7. Subsequently, they will be removed entirely.

Numpy team has done it. numpy/numpy#10743

if PY33:
    import collections.abc as collections_abc
else:
    import collections as collections_abc

A problem is collections_abc being too long, isinstance(something, collections_abc.Iterable) occupies half line, but from pandas.compat.collections_abc import Iterable might pollute namespace.

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BTW, pandas/compat/__init__.py seems messy. Since Much of the code in this module comes from Benjamin Peterson's six library, why not require six like many other libraries do?

[gfyoung]

@holymonson :

• The collections_abc proposal seems reasonable.
• As for six, I imagine it's because we only needed that chunk of code for __init__ and not everything else, though probably someone like @jreback would know more...

[jbrockmendel]

re six: it is an implicit dependency because dateutil requires it. It would simplify some of the intra-pandas dependencies if we got imports from six instead of pandas.compat.

[holymonson]

Since six provide some but not all compat things, keeping all import from pandas.compat seems more unified. What I suggest is from six import what's needed to pandas.compat, that will clean up code in pandas.compat.

[holymonson]

Being the last of the 2.x series, 2.7 will have an extended period of maintenance. Specifically, 2.7 will receive bugfix support until January 1, 2020. All 2.7 development work will cease in 2020.

The End Of Life date of Python 2 is 2020-01-01, let's forget six and clean up the code in the future.

[gfyoung]

@holymonson : I still think your collections proposal is reasonable though. Feel free to do a PR for that.

[TomAugspurger]

We're planning to remove 2.7 support at the end of the year. If somewhat absolutely needs Python 3.8 support before then, they're welcome to update pandas/compat/__init__.py to handle this. Otherwise, I'd recommend waiting until January when we remove Python 2 compatibility code, and we can just update the imports to collections.abc.