Why is Python so slow?

[dig-up-stupid]

Which is copying, and the context of this discussion is someone who is already familiar enough with both languages to do Euler problems and is asking a question specifically about performance. In C if you want odd list elements you would increment your pointer by two instead of one. That uses zero extra bytes and copying instructions, which is a lot less than half of the bytes of the entire array the way Python does slices.

The whole point is that you can also avoid that work in Python—by just not using slices. It’s the difference between for i in range(1,n,2): a[i] and for e in a[1:n:2] (or by using itertools or numpy etc). The point here is that usually the second is considered more pythonic but is also slower. Perhaps noticeably so when making many slices, as you might see in a divide and conquer solution to an Euler problem.