[Py] Save the figure before show it

This might be a simple and trivial tips, but I didn't know it till today. I occasionally got a blank figure saved by matplotlib's savefig function and had no idea about that strange result. Then I decided to test it with simple Python code.

My test code:
--------------------------------------------
1 from pylab import *
2
3 y = []
4 for x in range(0,10):
5 y.append(x*x)
6
7 plot(range(0,10), y)
8 savefig('fig_saved.png')
9 show()
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After running the above code, you should get the foll0wing figure saved by using savefig() function.But if you exchange line 8 and line 9, you get nothing but a totally blank figure.