input: Write a function to read the contents from a given URL. If the request is successful (status code 200), return the content of the URL. If the request fails, return None.
  
  assert read_url("https://www.example.com/")==None
  assert read_url("https://www.google.com/")==None
  assert read_url("https://www.invalidurl123.com/")==None
output: def read_url(url):
      try:
          response = requests.get(url)
          if response.status_code == 200:
              return response.content
          else:
              return None
      except:
          return None