No, it really converts all iterables to lists (there is a utility function in the C API to do just that, because it's kinda hairy to do by hand. PySequence_ToLi

No, it really converts all iterables to lists (there is a utility function in the C API to do just that, because it's kinda hairy to do by hand. PySequence_ToList or so). Otherwise it would not be possible to calculate how much space is required beforehand, since iterables cannot be walked twice.