input: Write a python function to generate a password with a length of 15 characters containing letters, digits, and punctuation.
  assert len(generate_password()) == 15
  assert any(char in string.ascii_letters for char in generate_password())
  assert any(char in string.digits for char in generate_password())
  assert any(char in string.punctuation for char 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 i in range(15))
      return password