BF - prevent a TypeError for lists of vertices in set_marker

[ajdawson]

The documentation for setting markers (http://matplotlib.org/api/artist_api.html#matplotlib.lines.Line2D.set_marker) suggests that:

a list of (x, y) pairs used for Path vertices

is an acceptable input. However, if one tries to use a Python list a TypeError is returned. This is because the set_marker code attempts to use the marker specification as the key in a dictionary, which fails because lists are not hashable. To avoid this I added an extra condition to the logic that makes sure the input is not a list before attempting to use it as a dictionary key (taking advantage of lazily evaluated boolean conditions). This allows the final conditional to be executed which happily constructs a path from a list of vertices, just as it does from a tuple of vertices.

[pelson]

Thanks @ajdawson - would you be able to add a test? (updating an existing test, if appropriate, would be fine)

[ajdawson]

I added a new test in test_axes.py, it seemed the most appropriate option.

[ajdawson]

OK I've used extensions=['png'] and removed the pdf and svg test images. I overwrote the test image with one that contains no text without thinking about it. The test function is written so that it would produce text, but has remove_text=True in the image comparison decorator, so I guess this is OK?

[dmcdougall]

In my opinion, this is fixing a bug and should target v1.2.x. What do others think?

[efiring]

Yes, it is fixing a bug.

[ajdawson]

I made a new PR #1854 that introduces this change into the v1.2.x branch.