input: from typing import Optional
  import requests
  
  def read_url(url: str) -> Optional[str]:
      """Reads the contents from a given URL and returns the text if the request is successful.
      If the request fails, it returns None.
      >>> read_url('https://www.example.com')
      '<!doctype html>\n<html>\n<head>\n...'
      >>> read_url('https://www.nonexistentwebsite.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