[Matplotlib-users] Novice question: Am I using pyplot.rgrids correctly?

[Bob D. <rjd...@ca...>]

I am a matplotlib.pyplot novice, but I have looked through various FAQs 
to no avail.

I am plotting a polar graph with some negative values of r.  Everything 
goes well until I try to use rgrids().  Am I doing something wrong?

I attach some demo scripts and their outputs.

version1.py uses rgrid() but only has positive values of r.  Everything 
works the way I expect it to (see version1.png).

version2.py has negative values of r and the same call to rgrid() and 
misbehaves (see version2.png).

version3.py is the same as version2.py, but without the call to rgrids() 
(but with negative values of r).  Again everything is as expected.

What am I doing wrong in version2.py?