Note that using exceptions for control flow can be bad for other implementations of Python. For example exceptions on the .NET framework are very expensive.
Why do you say that? What specific implementation of .NET are you referring to? What do you mean by "very"?
Isn't it better practise for exceptions to be used for exceptional circumstances rather than for control flow?
This is an ongoing debate (in Python, and outside). I'm in the camp that says that exceptions are a control flow mechanism just like loops, conditionals, and recursion. With exceptions, you get essentially multiple alternative outcomes of a function call, rather than just a single result. In principle, it would be possible to eliminate the return statement altogether, but it is useful syntactic sugar. Regards, Martin