Can't get plot from PyCharm 2.7.3 to remain visible.

Hello -

I am trying to plot from PyCharm 2.7.3.  I have imported pyplot and created a figure using pyplot.  The figure exists as a 400x400 image, and I can make it visible with fig.show(), but it vanishes immediately.  I also tried pyplot.imshow, but again with no success.  I would appreciate any pointers you would care to share with me.  I suspect I've overlooked something obvious.

Thank you.

David