problem with show()


I'm learning how to use matplotlib and I'm having a problem with show().
I did the simplest example of the Tutorial on the Matplotlib's homepage:

from matplotlib.matlab import *

It works fine, but when I try to run it again (second time on the same
session), the plot is not shown. I have another question too: when I run
the show() command, my program stops and only continues when I close the
plot windows. Is there anyway of show the plot and continues the program
with the plot window openned?

I'm using matplotlib 0.64.4-1 on a Debian GNU/Linux.

Sorry about my poor english.