WxAgg hangs in interactive mode

[BrenBarn]

I'm using 64-bit Windows 7 with matplotlib 1.2.0 and WxPython 2.8.12.1. I
was fiddling around with some of the different backends to see what
they look like and I found that the WxAgg backend doesn't work interactively:

Python 2.7.3 (default, Apr 10 2012, 23:24:47) [MSC v.1500 64 bit 
(AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
 >>> import matplotlib as mpl
 >>> mpl.use('WxAgg')
 >>> from matplotlib import pyplot
 >>> pyplot.ion()
 >>> pyplot.plot([1, 2, 3])
[<matplotlib.lines.Line2D object at 0x0000000006757DA0>]
 >>>

When I do the plot, the figure windows appears, but it's blank (without even a proper blank background, just the white area you get when a program goes on the fritz) and immediately shows "Not responding". I have to kill the window, and doing so crashes the Python session. However, it works without the "ion()" call: I can then call show() and see the plot fine.

I have wxPython working fine in other apps. In fact, what's especially odd is that I actually have an app that directly uses FigureCanvasWxAgg to embed matplotlib graphs in a GUI, and this seems to work fine. So it seems the problem is somehow in matplotlib's own management of the interactive figure window.

There was a previous question about a similar WxAgg issue on the list ( http://matplotlib.1069221.n5.nabble.com/trouble-with-show-not-drawing-in-interactive-mode-w-WxAgg-td39110.html ), but there was no real answer: the poster just decided not to use WxAgg. But aren't we really supposed to be able to use WxAgg interactively?

[pelson]

Thanks for raising @BrenBarn.

[cgohlke]

I can reproduce this issue. The same happens with the Wx backend. Looks like the event loop is not running.

[efiring]

The event loop is not running on Linux either unless one uses ipython --pylab=wx. I don't know that we ever guaranteed interactive support without IPython's help, though. IPython installs a custom PyOS_InputHook, and the one for wx is particularly elaborate. We have always left fiddling with the InputHook to IPython. All the ion() call does is to set a flag so that pyplot functions automatically draw. I think the other backends work without IPython because they have adequate PyOS_InputHook functions by default.

[efiring]

Based on my previous comment, I am removing the milestone and closing this.