Merge sort implemented in Python 3

mergesort.py

def mergesort(c):
  if len(c) > 1:
    pivot = len(c)//2
    a = c[:pivot]
    b = c[pivot:]
    mergesort(a)
    mergesort(b)
    ap = 0
    bp = 0
    cp = 0
    while ap < len(a) and bp < len(b):
      if a[ap] < b[bp]:
        c[cp] = a[ap]
        ap += 1
      else:
        c[cp] = b[bp]
        bp += 1
      cp += 1

    while ap < len(a):
      c[cp] = a[ap]
      ap += 1
      cp += 1

    while bp < len(b):
      c[cp] = b[bp]
      bp += 1
      cp += 1

if __name__ == "__main__":
  from sys import argv
  from random import shuffle

  list = list(range(int(argv[1])))
  shuffle(list)
  mergesort(list)
  print(all(list[i] <= list[i+1] for i in range(len(list)-1)))