input: Write a function to generate a random string of a specified length. The function should utilize Python's random and string modules to create the string, which should consist entirely of lowercase alphabetic characters.
  assert random_string(6) != random_string(6)
  assert len(random_string(6)) == 6
  assert all(c in string.ascii_lowercase for c in random_string(6))
output: def random_string(length):
      import random
      import string
      return ''.join(random.choice(string.ascii_lowercase) for _ in range(length))