On Saturday, May 5, 2012, Tony Yu wrote:
> I'm getting a strange error when multiple figures are created *without a
> call to show*. Here's the traceback:
>
> Traceback (most recent call last):
> File
> "/Users/Tony/python/devel/mpl/lib/matplotlib/backends/backend_qt4.py", line
> 151, in <lambda>
> lambda: self.close_event())
> File "/Users/Tony/python/devel/mpl/lib/matplotlib/backend_bases.py",
> line 1564, in close_event
> self.callbacks.process(s, event)
> AttributeError: 'FigureCanvasQTAgg' object has no attribute 'callbacks'
>
>
> Here's a simple test case:
>
> import matplotlib.pyplot as plt
> fig = plt.figure()
> plt.plot([0, 1])
> fig = plt.figure()
> plt.plot([0, 1])
>
>
> This issue appears in versions after the PR to fix the Qt4 close bug<https://github.com/matplotlib/matplotlib/pull/716>.
> The error occurs even without the `plot` calls, but the failures aren't as
> consistent (the error will randomly disappear).
>
> Note that sticking a call to `plt.show()` at the end and then manually
> closing the figures does not seem to produce this error. I'm having a
> difficult time locating the source of the bug: when I stick a pdb trace in
> the code, the error doesn't get raised.
>
> Can anyone reproduce this issue?
>
> -Tony
>
My gut tells me it is a race condition. Pdb can make race conditions
disappear because of all the overhead screws around with the timings.
Haven't tried reproducing it yet, though.
Ben Root
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