input: def read_url(url: str) -> str:
      """ Read the contents from a given URL.
      >>> read_url('https://www.example.com')
      '<html><head><title>Example Domain</title></head><body><h1>Example Domain</h1><p>This domain is for use in illustrative examples in documents. You may use this domain in literature without prior coordination or asking for permission.</p></body></html>'
      >>> read_url('https://www.nonexistenturl.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