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Block Spam Calls and Robocalls with Python

Block spam calls with Python

Spam, scams, and robocalls are at best annoying. For high-volume customer service centers, they can significantly impact the bottom line. Let’s leverage the Twilio Marketplace and our Python skills to block spam callers, robocallers, and scammers.

Before getting started, you should already know how to handle incoming calls with Twilio.

Let's get started!

Get a Spam Filtering Add-on

The Twilio Add-ons Marketplace is a great place to find Add-ons for your Twilio apps. You can integrate third-party technologies without leaving the comfort of the Twilio API. You can access the Add-ons from your Twilio Console. Today, we’re going to look at a few Voice Add-ons that can help us with this spam problem. They are, in no particular order, Whitepages Pro Phone Reputation, Marchex Clean Call, and Nomorobo Spam Score:

Voice Spam Add-ons

We’ll be writing code to work with all three of these Add-ons, but you can research which one you think will work best for your requirements. Also, keep an eye on the Marketplace, as new Add-ons are always showing up.

How to install any Add-on

Installing the Add-on

Once you’ve decided on the Add-on you’d like to use, click the

Install
button and agree to the terms. In our use case today, we want to make use of these Add-ons while handling incoming voice calls, so make sure the “Incoming Voice Call” box for “Use In” is checked and click “Save” to save any changes:

Use in incoming voice call

Note the “Unique Name” setting. You need to use this in the code that you will write to read the Add-on’s results. In the code for this guide, we are sticking with the default names.

Now let's check out how to implement an application using those Add-ons

Check Phone Number Score in Python

When Twilio receives a phone call from your phone number, it will send details of the call to your webhook (more on how to configure that later). In your webhook code, you create a TwiML response to tell Twilio how to handle the call.

For spam-checking, our code needs to check the spam score of the number and deal with the call differently depending on whether the Add-on considers the caller to be a spammer or not. In our example code here, we’ll return a TwiML tag to send spammers packing and a TwiML tag to welcome legit callers.

The code is a simple Flask application:

        
        
        
        
        Flask application using Add-Ons to automatically filter spam calls

        Block Spam Calls with Python

        Flask application using Add-Ons to automatically filter spam calls

        Notice the code has checks for all three of the Add-ons we mentioned before. The code is written to be very flexible and handle missing data in the JSON response, so feel free to copy and paste even if you only plan to use one of the Add-ons. Next, we'll analyze this application in more details.

        How do we use Whitepages Pro?

        How to Check Whitepages Pro Phone Reputation

        Here’s an example of what Whitepages Pro Phone Reputation will return in the “AddOns” form parameter:

              
              
              
              

              Parsing that data in Python is done as follows:

                    
                    
                    
                    
                    Make sure the Add-on processed successfully the call and use the Reputation in order to decide to block, or not, the call

                    Decide to block the call based on White Pages Pro

                    Make sure the Add-on processed successfully the call and use the Reputation in order to decide to block, or not, the call

                    This function uses only information found in the key results.whitepages_pro_phone_rep. Here we advise blocking the call if the reputation's level is 4.

                    How do we use Marchex Clean Call?

                    How to Check Marchex Clean Call

                    Here’s an example of what Marchex Clean Call will return:

                          
                          
                          
                          

                          Working with that data in Python can be handled with:

                                
                                
                                
                                
                                Make sure the Add-on processed the call successfully and followed Marchex' recommendation to decide to block, or not, the call

                                Decide to block the call based on Marchex Clean Call

                                Make sure the Add-on processed the call successfully and followed Marchex' recommendation to decide to block, or not, the call

                                This function uses only information found in the key results.marchex_cleancall. Here we advise blocking the call if Marchex' recommendation is set to BLOCK.

                                How do we use Nomorobo Spam Score?

                                How to Check Nomorobo Spam Score

                                Here’s an example of what Nomorobo Spam Score will return:

                                      
                                      
                                      
                                      

                                      Finally, handling that data in Python:

                                            
                                            
                                            
                                            
                                            Make sure the Add-on processed the call successfully and checked Nomorobo Spam Score to decide to block, or not, the call

                                            Decide to block the call based on Nomorobo Spam Score

                                            Make sure the Add-on processed the call successfully and checked Nomorobo Spam Score to decide to block, or not, the call

                                            This function uses only information found in the key results.nomorobo_spamscore. Here we advise blocking the call if Nomorobo Spam Score is 1.

                                            Now we've seen how to get advice from each Add-on. But we may have differents opinions for the same call, let's look at how we're taking the final decision.

                                            How do we finally to decide to block a call?

                                            Making a decision

                                            In our example, unanimity is required for accepting a call. So for each Add-on, we look at their advice, and if even one of them tells us to block it, we'll reject the call.

                                                  
                                                  
                                                  
                                                  
                                                  Decide to accept the call only if all Add-ons are unanimous

                                                  Make a decision on blocking the call or not from all the Add-ons

                                                  Decide to accept the call only if all Add-ons are unanimous

                                                  We could have also implemented it differently by using a majority rule. In any case, once we make a decision, all that is left to do is to act.

                                                  What are our options to accept or reject a call?

                                                  Call Handling Options

                                                  Rejection Options

                                                  Using <Reject> is the simplest way to turn away spammers. However, you may want to handle them differently. The whole universe of TwiML is open to you. For example, you might want to record the call, have the recording transcribed using another Add-on, and log the transcription somewhere for someone to review.

                                                        
                                                        
                                                        
                                                        

                                                        Call Accept Options

                                                        For this example, we’re just greeting the caller. In a real-world scenario, you would likely want to connect the call using <Dial> (to call another number or Twilio Client), <Enqueue> the call to be handled by TaskRouter, or build an IVR using <Gather>.

                                                              
                                                              
                                                              
                                                              
                                                              How do we set up this application and test it?

                                                              Configuring a Phone Number Webhook

                                                              Now we need to configure our Twilio phone number to call our application whenever a call comes in. So we just need a public host for our application. You can serve it any way you like as long as it's publicly accessible or you can use ngrok to test locally.

                                                              Armed with the URL to the application, open the Twilio Console and find the phone number you want to use (or buy a new number). On the configuration page for the number, scroll down to "Voice" and next to "A CALL COMES IN," select "Webhook" and paste in the function URL. (Be sure "HTTP POST" is selected, as well.)

                                                              Webhook - ngrok - root

                                                              Everything is set up now, you can pick up your phone and call your Twilio number. Hopefully, if you are not a spammer your call should be accepted and you should hear the greeting.

                                                              How can I test a blocked call?

                                                              Testing a Blocked Call

                                                              You can quickly call your Twilio number to make sure your call goes through. However, how can we test a blocked spam result? The easiest way is to write some unit tests that pass some dummied up JSON to our controller action. For example, if we wanted to test a Nomorobo “BLOCK” recommendation, we could use the following JSON:

                                                                    
                                                                    
                                                                    
                                                                    

                                                                    With that as our test fixture, we can write a test like the following to ensure that our call is blocked when we see the right data in the AddOns JSON:

                                                                          
                                                                          
                                                                          
                                                                          
                                                                          Uses the previous fixture to ensure we block a call not recommended by Nomorobo

                                                                          Testing a blocked call with Nomorobo

                                                                          Uses the previous fixture to ensure we block a call not recommended by Nomorobo
                                                                          What's Next?

                                                                          What’s Next?

                                                                          As you can see, the Twilio Add-ons Marketplace gives you a lot of options for extending your Twilio apps. Next, you might want to dig into the Add-ons reference or perhaps glean some pearls from our other Python tutorials. Wherever you’re headed next, you can confidently put spammers in your rearview mirror.

                                                                          Samuel Mendes Jose Oliveros Agustin Camino Jyden Tyree David Prothero Kat King Craig Dennis
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