input: def read_url(url: str) -> str:
      """Read the contents from a given URL and return the content as a string.
      If the URL is not accessible, return None.
  
      >>> read_url('https://www.google.com')
      '...lots of HTML code...'
      >>> read_url('https://www.nonexistentwebsite.com')
      None
      """
      import requests
      r = requests.get(url)
      if r.status_code == 200:
          return r.text
      else:
          return None
output:     import requests
      r = requests.get(url)
      if r.status_code == 200:
          return r.text
      else:
          return None