Re: [Matplotlib-users] Matplotlib 1.1.0 animation vs. contour plots

[Benjamin R. <ben...@ou...>]

On Sunday, November 13, 2011, Daniel Hyams <dh...@gm...> wrote:
>>
>> OK, types is a new part of the Python library for me, I'll have to go
>> learn about it.  It looks like you basically just subclassed the
>> QuadContourSet object through a back door, by giving it the missing
>> method.
>
> It's not a subclass, it's just a "monkey patch".  I personally like
> "duck punching", because even just reading the term makes me laugh:
> "If it walks like a duck and quacks like a duck, it's a duck; or if it
> does not walk or talk like a duck, punch it until it does".  In this
> case, we're punching the QuadContourSet until it behaves like an
> Artist.  It's a useful technique for experimenting, and can be used as
> a patching technique in the interim until it is fixed properly.  You
> never want to write code like this on a regular basis, however.
>
>
>> Your patch solves one of two animation problems, and I offer a
>> suggestion about how to fix the second (with questions).
>>
>> The program gets as far as ani.save() on line 29 without generating any
>> errors. An MP4 file showing animated contours is written to disk.  The
>> origin of the contour plot is in the lower left, versus the upper left
>> of the original imshow() call, but that's expected.
>>
>> When you get to plt.show() on line 31, however:
>>
>> Traceback (most recent call last):
>>  File
>>
"/usr/local/lib/python2.6/dist-packages/matplotlib/backends/backend_gtk.py",
line 127, in _on_timer
>>    TimerBase._on_timer(self)
>>  File
>> "/usr/local/lib/python2.6/dist-packages/matplotlib/backend_bases.py",
>> line 1091, in _on_timer
>>    ret = func(*args, **kwargs)
>>  File "/usr/local/lib/python2.6/dist-packages/matplotlib/animation.py",
>> line 317, in _step
>>    still_going = Animation._step(self, *args)
>>  File "/usr/local/lib/python2.6/dist-packages/matplotlib/animation.py",
>> line 179, in _step
>>    self._draw_next_frame(framedata, self._blit)
>>  File "/usr/local/lib/python2.6/dist-packages/matplotlib/animation.py",
>> line 199, in _draw_next_frame
>>    self._post_draw(framedata, blit)
>>  File "/usr/local/lib/python2.6/dist-packages/matplotlib/animation.py",
>> line 222, in _post_draw
>>    self._blit_draw(self._drawn_artists, self._blit_cache)
>>  File "/usr/local/lib/python2.6/dist-packages/matplotlib/animation.py",
>> line 236, in _blit_draw
>>    bg_cache[a.axes] = a.figure.canvas.copy_from_bbox(a.axes.bbox)
>> AttributeError: QuadContourSet instance has no attribute 'figure'
>
> It looks like just one more duck punch is needed; just set
>
> im.figure = fig
>
> after the setting of im.axes.  QuadContourSet should really call
> a.get_axes() and a.get_figure() instead of using the attributes
> directly; doing so would allow any object that implements the proper
> interfaces to work, artist or no.
>
>> Is this error occurring because there is no bit-mapped representation of
>> a contour object?
>
> It's not really that, it's just that the animation class expects to be
> given a list of Artists to work with (the original author can correct
> me if I'm wrong), and that's not what it is being given, because a
> QuadContourSet is not an Artist.  But you can duck punch it until it
> acts like one :D
>
> IMO, there are quite a few things in matplotlib that are a little
> inconsistent in this way.
>

"duck-punching"

Is that an official term? I have done things like this before, but never
had a word for it.

Ben Root