Cheap exception handling in Python?

I read in an earlier answer that exception handling is cheap in Python so we shouldn't do pre-conditional checking.

I have not heard of this before, but I'm relatively new to Python. Exception handling means a dynamic call and a static return, whereas an if statement is static call, static return.

How can doing the checking be bad and the try-except be good, seems to be the other way around. Can someone explain this to me?