Well, this is a good question, everyday I read news about python I keep surprising about the power of the language. I think there is a lot you can do, and almost nothing you can't do with it.
But... if I have to make a list of what I wouldn't use python for, I'll say...
- Game programming. Althought you can use pygame libraries to create great 2d games, or others libraries (Cocos, Panda) or low level game programming (Pyglet, PyOpenGl).
- OS programming.
- Mobile programming. Nowadays you have libraries like Kivy which indeed are great for touchables environments.
- Low memory/cpu consumption apps. By this I mean, when I have to code in a old PC, I prefer using C++.
This is a list of what I think python is not suitable.