Python sorting complexity on sorted list

Question

What is the sort(already_sorted_list) complexity in Python? Does Python check if given iterable is sorted, or do I have to do it by myself? I could not find it anywhere in the docs.

Answer 1

This is entirely implementation dependent. All that python guarantees is that the builtin sorting algorithm is stable (elements which compare equal retain their relative ordering). An implementation could even use a stable bubble sort if it wanted to ...

Cpython uses TimSort (a hybrid of insertion sort an mergesort) which I believe has O(N) complexity if the input is already sorted -- It picks up the best case performance of insertion sort and the worst case performance of mergesort (O(NlogN)).

And if you're curious about the implementation, the source code has a very nice description.

Answer 2

Python's sort is called timsort . Its average case performance is O(nlog(n)). It performs really well with pre-sorted lists because it's implementation is designed to seek out runs of sorted elements in the list.