To block spam calls and robocalls using Python with Twilio, you need to integrate third-party technologies such as Marchex Clean Call and Nomorobo Spam Score into your Twilio application. You can use these add-ons through the Twilio Console and configure them to send data to your webhook, which then checks the spam score of the caller and rejects or accepts the call accordingly. The decision-making process is based on a majority vote among the add-ons, with any single add-on advising against blocking being overridden by another. You can customize the call handling options, such as rejection or acceptance, using TwiML tags. Once configured, you can test your application by calling your Twilio number and verifying that it handles spam calls correctly.