Agreed about C/C++/JS, though I'm curious to hear your thoughts about Python. There are only two really common gotchas in Python that I tend to notice:
- Using an iterator more than once silently produces nothing. I notice this when I insert print statements to debug something, but then accidentally turn the following for-loop into a no-op. The Python 3 change that made more top-level functions return iterators made this problem more common, though I agree with the performance justification for doing it. It would be nice if iterating again after hitting the end raised an Exception, though I'm sure that would break all sorts of code that assumes it doesn't.
- Mutating function default arguments affects all subsequent calls. This is most common Python gotcha people seem to talk about.
