input: def read_url(url: str) -> str:
      """Read the contents from a given URL using the requests library.
      Returns the content as a string if the request is successful (status code 200),
      otherwise returns None.
      >>> read_url("https://www.google.com")
      '<!doctype html>...</html>'  # Truncated for brevity
      >>> 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