input: Write a python function to generate a random password of 12 characters.
  assert len(generate_password()) == 12
  assert any(c.isdigit() for c in generate_password())
  assert any(c.isupper() for c in generate_password())
  assert any(c in string.punctuation for c in generate_password())
output: import random
  import string
  
  def generate_password():
      characters = string.ascii_letters + string.digits + string.punctuation
      password = ''.join(random.choice(characters) for _ in range(12))
      
      while (not any(c.isdigit() for c in password) or
             not any(c.isupper() for c in password) or
             not any(c in string.punctuation for c in password)):
          password = ''.join(random.choice(characters) for _ in range(12))
      
      return password