input: 
  import requests
  
  def read_url(url: str) -> str:
      """ Retrieve the content from the given URL and return it as a string.
      If the request is unsuccessful, return None.
  
      >>> read_url('https://www.example.com')
      '<!doctype html><html>... (content of the example.com)'
      >>> read_url('https://www.nonexistenturl.com')
      None
      """
      r = requests.get(url)
      if r.status_code == 200:
          return r.text
      else:
          return None
  
output:     r = requests.get(url)
      if r.status_code == 200:
          return r.text
      else:
          return None