input: Write a python function to generate a random string of length 5.
  assert len(generate_random_str()) == 5
  assert isinstance(generate_random_str(), str)
  assert generate_random_str() != generate_random_str()
output: import random
  import string
  
  def generate_random_str():
      return ''.join(random.choices(string.ascii_letters + string.digits, k=5))