code: def random_str(Nchars=6, randstrbase='0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ'):
      
      return ''.join([randstrbase[random.randint(0, len(randstrbase) - 1)] for i in range(Nchars)])
docs: Return a random string of <Nchars> characters. Characters are sampled
      uniformly from <randstrbase>.