[throwaway894345]

Your conclusion might be right, but your reasoning is certainly wrong. Calling native functions in Python is often quite expensive because you need to marshal between PyObjects and the native types (probably allocating memory as well). This doesn’t “feel” so slow in Python because, well, everything in Python is slow. But you really start to notice it when you’re optimizing.

[ahupp]

Of course "It depends", but in my experience that kind of thing is rare. Either you're passing in str and can just grab the char* out of the existing PyObject, or you have some more complicated thing that was wrapped once in a PyObject and doesn't need to be converted, etc. But sure, if you have some dict with a lot of data and need to convert it into an std::map you'll have a bad time.