input: Write a python function to generate a random password.
  assert len(generate_password(8)) == 8
  assert len(generate_password(12)) == 12
  assert len(generate_password(0)) == 0
output: import random
  import string
  
  def generate_password(length):
      if length == 0:
          return ''
      characters = string.ascii_letters + string.digits + string.punctuation
      password = ''.join(random.choice(characters) for _ in range(length))
      return password