input: Write a python function to generate a random password of length 6 containing both letters and digits.
  assert len(random_password()) == 6
  assert any(c.isalpha() for c in random_password())
  assert any(c.isdigit() for c in random_password())
output: import random
  import string
  
  def random_password():
      letters_and_digits = string.ascii_letters + string.digits
      password = ''.join(random.choice(letters_and_digits) for _ in range(6))
      return password