Python - Merge Sort

import randomdef merge(arr, l, p, r):    left = arr[l: p+1] #copy left part, including p    right = arr[p+1: r+1] #copy right part, start from p+1    i = 0    j = 0    k = l #start from the left    while i < len(left) and j < len(right):        if left[i] < right[j]:            arr[k] = left[i]            i = i + 1        else:            arr[k] = right[j]            j = j + 1        k = k + 1    while i < len(left):        arr[k] = left[i]        i = i + 1        k = k + 1    while j < len(right):        arr[k] = right[j]        j = j + 1        k = k + 1def merge_sort(arr, l, r):    if l < r:        p = int((l + r) / 2)        merge_sort(arr, l, p) #sort [1, p]        merge_sort(arr, p+1, r) #sort[p + 1 ... end]        merge(arr, l, p, r)        if __name__ == '__main__':    sample = [random.randrange(0, 100, 1) for i in range(10)]    original = sample[:]    print('Before: %s'%original)    merge_sort(sample, 0, len(sample)-1)    print('After: %s'%sample)    print('Corrected: %s'%(sample == sorted(original)))