There was a bug report recently (not to the mailing list) where the reporter
noted that if an Axes3D was created using the fig.add_subplot(111,
projection='3d') or fig.gca(projection='3d'), then you can not clear the
figure using fig.clf(). Doing so causes an exception to be thrown.
Tracing down the problem revealed that the Axes3D object was added twice to
the figure's self.axes, but exists only once in self._axstack. So, when
looping through self.axes, a delete is attempted on an axes that no longer
exists in the stack.
I traced down the cause for why the axes is added twice. Because of how
Axes3D used to be attached to a figure (and is still valid), the __init__()
function for Axes3D calls figure.add_axes(self) on its own. This
initialization is done after the check in add_subplot to see if the axes
exists already in the figure. So, add_subplot then adds the axes without
knowing that it already happened.
I think there are multiple issues here. Primarially, there is the issue
that Axes3D is attaching itself to a figure. However, in the interest of
backwards-compatibility, we can't just fix this outright. There is also the
issue that there are multiple places in the Figure class that are adding
axes to the figure object. Ideally, shouldn't we have a single function
that performs proper checks and adds an axes? Then that function should be
used in the other class functions to perform this action. In my opinion,
there is too much duplicated code here.
Thoughts, concerns, ideas?
Ben Root
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