input: Write a function to generate a random password of length 8, which consists of alphanumeric characters and at least one special character. The function should be named `generate_password`.
  
  assert generate_password()!=''
  assert len(generate_password())==8
  assert any([char in string.punctuation for char in generate_password()])==True
output: import random
  import string
  
  def generate_password():
      while True:
          password = ''.join(random.choices(string.ascii_letters + string.digits + string.punctuation, k=8))
          if any(char in string.punctuation for char in password):
              return password