input: Write a function to generate a random string of a specified length. The function should return a string composed of lowercase letters.
  
  def random_string(length):
      letters = string.ascii_lowercase
      return ''.join(random.choice(letters) for i in range(length))
      
  assert random_string(6) in string.ascii_lowercase * 3
  assert len(random_string(6)) == 6
  assert type(random_string(6)) == str
output: import random
  import string
  
  def random_string(length):
      letters = string.ascii_lowercase
      return ''.join(random.choice(letters) for i in range(length))