Are there any downsides in Python to using a library that is just a binding to a C library? Does that hurt the portability of your application? Anything else I should look out for?
Portability is one thing. There are even differences between python 2.x and 3.x that can make things difficult with C extensions, if the writer didn't update them.
Another thing is that pure python code gives you a bit more possibilities to read, understand and even modify (although it is usually a bad sign if you need to do that for other peoples modules)
What are the pros and cons in Python of using a c library vs a native python one