input: Write a function to generate a random password of length 8 using a set of given letters, numbers, and special characters. If no input is provided, use the default set of characters. Return the generated password as a string.
  assert generate_random_password()!="password123"
  assert len(generate_random_password())==8
  assert generate_random_password().isalnum()==False
  assert generate_random_password().islower()==False
  assert generate_random_password().isupper()==False
output: import random
  
  def generate_random_password(chars=None):
      if chars is None:
          chars = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789!@#$%^&*()_+"
      return ''.join(random.choice(chars) for _ in range(8))