input: Write a function to read the contents from a given URL. If the request is successful (i.e., the status code is 200), return the text content of the page; otherwise, return None.
  import requests
  
  def read_url(url):
    r = requests.get(url)
    if r.status_code == 200:
      return r.text
    else:
      return None
  
  assert read_url('https://www.google.com') is not None
  assert read_url('https://www.example-not-exist.com') is None
output: import requests
  
  def read_url(url):
    r = requests.get(url)
    if r.status_code == 200:
      return r.text
    else:
      return None