input: def read_url(url: str) -> str:
      """Read the contents from a given URL and return the text if the request is successful.
      If the request fails, return None.
      >>> read_url('https://www.example.com')
      '<!doctype html><html><head><title>Example Domain</title>...</head><body>...</body></html>'
      >>> 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