input: def read_url(url: str) -> str:
      """Read the contents from a given URL
      >>> read_url('https://www.example.com')
      '<!doctype html>\n<html>\n<head>\n<title>Example Domain</title>\n...</html>'
      >>> read_url('https://www.nonexistentwebsite.com')
      None
      """
      r = requests.get(url)
      if r.status_code == 200:
          return r.text
      else:
          return None
output:     import requests