How to correctly measure time and operations of sorting algorithms in Python

I've tried to count the done operations in a algorithm the following way

def selection_sort(arr):
    ops = 0  # The number of done operations
    for i in range(0, len(arr)):
        ops += 1
        least_idx = i
        ops += 1
        for j in range(i, len(arr)):
            ops += 1
            if arr[j] < arr[least_idx]:
                ops += 1
                least_idx = j
                ops += 1
        arr[i], arr[least_idx] = arr[least_idx], arr[i]
        ops += 3
    return ops

Is it correct? And if it is, how to do it for a recursive algorithm like merge sort? And as for the runtime, I'm afraid that caching of the previous results will impact the next ones. The testing process is the following:

from random import sample

sort_algos = [selection_sort, insertion_sort, merge_sort]
for algo in sort_algos:
    for n in range(7, 8):
        arr = sample(range(0, 2**n), 2**n)
        algo(arr)

And in the end I want to have measures of the results for each n. Thank you in advance.