input: Write a function to generate a random password given a set of letters, numbers, and characters. The function should return the generated password as a string.
  
  assert generate_password()==some_password
  assert len(generate_password())==8
output: import random
  import string
  
  def generate_password():
      characters = string.ascii_letters + string.digits + string.punctuation
      return ''.join(random.choice(characters) for _ in range(8))