MAINT: mappingview check for Python 3.4

[matthew-brett]

Python 3.4 does not autoamatically import module abc into
collections, causing an error when checking for
collections.abc.MappingView. Do more explicit import of MappingView
to work round this difference.

See: https://travis-ci.org/MacPython/matplotlib-wheels/jobs/205713297#L582 for
error on Python 3.4.

[phobson]

Looks like the except block only applies to python 2.7, is that right?

[anntzer]

2.7 has mappingview (https://docs.python.org/2.7/library/collections.html#collections.MappingView) so I don't know when it can ever be triggered.

(My guess is that below, the test on whether we're running Py3 should just be removed -- we may as well sanitize the case where someone passes dic.itervalues() on Py2 too (well I always thought the whole idea was misguided but let's at least be consistent across Python versions.))

[matthew-brett]

So - collections.MappingView is present in all Python versions we support, but collections.abc.MappingView is present only for the Python 3 versions:

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 as well.

https://docs.python.org/3.5/library/collections.html#module-collections

We could use collections.MappingView directly, they haven't been deprecated, I guess.

[story645]

I vote for using collections.MappingView directly then as I think the if MappingView = None is clunky

[matthew-brett]

Done.

[matthew-brett]

Right but I also felt it expressed the intention more clearly.

…

On 28 Feb 2017 16:19, "Paul Hobson" ***@***.***> wrote: ***@***.**** approved this pull request. ------------------------------ In lib/matplotlib/cbook/__init__.py <#8166 (comment)> : > @@ -13,6 +13,12 @@ from six.moves import xrange, zip from itertools import repeat import collections + +try: + from collections.abc import MappingView +except ImportError: + MappingView = None Looks like the except block only applies to python 2.7, is that right? — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#8166 (review)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AAEIHBZhTiK-yJZ1nYy5venuZyFMA2Cbks5rhLmEgaJpZM4MNbox> .

[phobson]

@matthew-brett totally. I just wanted to make sure I understood it properly since I don't have a py2.7 installation handy.

[anntzer]

2.7 has mappingview (https://docs.python.org/2.7/library/collections.html#collections.MappingView) so I don't know when it can ever be triggered.

(My guess is that below, the test on whether we're running Py3 should just be removed -- we may as well sanitize the case where someone passes dic.itervalues() on Py2 too (well I always thought the whole idea was misguided but let's at least be consistent across Python versions.))

[anntzer]

Side question: Codecov says this line is covered, so how was that never caught before in the CI? (Unfortunately Travis doesn't want to load for me right now.)

[matthew-brett]

I'm just guessing, but I suspect that some versions of Python 3.4 do an automatic import of abc in collections, and some do not. Here's an example that does not, on macOS:

$ python3.4
Python 3.4.2 (v3.4.2:ab2c023a9432, Oct  5 2014, 20:42:22) 
[GCC 4.2.1 (Apple Inc. build 5666) (dot 3)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import collections
>>> collections.abc
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'module' object has no attribute 'abc'

That's just a guess, because the behavior above is so for all the Python3.4s I could find.

[anntzer]

LGTM (conditional on tests passing).

[dstansby]

It looks like sanitize_sequence isn't present on 2.0.x, so no need for a backport.