drawstyle accepts anything as default rather than raising

[madphysicist]

Setup

matplotlib.__version__ = 1.5.1
matplotlib.__version__numpy__ = 1.6
Python 3.5.1, IPython 4.1.2 running under anaconda
OS: Red Hat 6.5

Matplotlib installed with conda install matplotlib.

Issue

Supplying invalid drawstyle parameter to plot (and possible others) does not raise an error. I would expect the following not to work, but it does:

>>> import matplotlib.pyplot as plt
>>> plt.plot(range(5), range(5), drawstyle='mwahahahahaha')

For contrast, trying the same thing with fillstyle raises the expected error:

>>> plt.plot(range(5), range(5), fillstyle='mwahahahahaha')
...
ValueError: Unrecognized fillstyle full left right bottom top none

Notes

The issue seems to be happening here:

matplotlib/lib/matplotlib/lines.py

Line 988 in 3ba9279

if self._drawstyle != drawstyle:

. I would submit a PR, but I am pretty sure that adding something like

drawstyles = ('default', 'steps', 'steps-pre', 'steps-mid', 'steps-post')
if drawstyle not in drawstyles:
    raise ValueError(' '.join(('Unrecognized drawstyle',) + drawstyles))

would mess up something or another. If not, I would be glad to make the change.

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[tacaswell]

That seems like a reasonable course of action. In the (near) future the plan is to use traitlets everywhere which will help with this sort of thing, but documenting what needs to be validated by code that validates them in probably a good thing.

[tacaswell]

Most importantly, if you add tests it will make sure the traitlets do not cause any regressions.

[madphysicist]

I just wasn't sure if there was additional parsing being done as for set_linestyle, which accepts both a linestyle and a drawstyle in the same string.