input: Write a python function to generate a random password of given length using alphanumeric characters.
  assert len(generate_random_password(10)) == 10
  assert len(generate_random_password(15)) == 15
  assert isinstance(generate_random_password(8), str)
output: import random
  import string
  
  def generate_random_password(length):
      characters = string.ascii_letters + string.digits
      return ''.join(random.choice(characters) for _ in range(length))