input:                         
  import requests
  
  def read_url(url: str) -> str:
    """ Reads the contents from a given URL.
    >>> read_url('https://www.example.com')
    '<!doctype html>\n<html>\n<head>\n    <title>Example Domain</title>...'
    >>> read_url('https://www.invalidurl123456.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