input: Write a function to generate a random password that consists of 8 characters. The password should include a combination of letters (both uppercase and lowercase) and digits. If the function is called multiple times, it should generate a unique password each time.
  assert generate_password() != generate_password()
  assert len(generate_password()) == 8
output: import random
  import string
  
  def generate_password():
      characters = string.ascii_letters + string.digits
      return ''.join(random.choice(characters) for _ in range(8))