input: Write a function to generate a random password of a given length, including special characters and numbers.
  assert len(generate_password(8))==8
  assert len(generate_password(10))==10
  assert len(generate_password(12))==12
output: import random
  import string
  
  def generate_password(length):
      characters = string.ascii_letters + string.digits + string.punctuation
      password = ''.join(random.choice(characters) for i in range(length))
      return password