Gather User Input via Keypad (DTMF Tones) in Python

In this guide, we'll show you how to gather user input during a phone call through the phone's keypad (using DTMF tones) in your Python application. By applying this technique, you can create interactive voice response (IVR) systems and other phone based interfaces for your users.

The code snippets in this guide are written using the Flask web framework and the Twilio Python SDK. Let's get started!

Set up your Flask application to receive incoming phone calls

This guide assumes you have already set up your web application to receive incoming phone calls. If you still need to complete this step, check out this guide. It should walk you through the process of buying a Twilio number and configuring your app to receive incoming calls.

Collect user input with the TwiML verb

The TwiML verb allows us to collect input from the user during a phone call. Gathering user input through the keypad is a core mechanism of Interactive Voice Response (IVR) systems where users can press "1" to connect to one menu of options and press "2" to reach another. These prompts can be accompanied by voice prompts to the caller, using the TwiML and verbs. In this example, we will prompt the user to enter a number to connect to a certain department within our little IVR system.

Use to collect user input via the keypad (DTMF tones)

1from flask import Flask
2from twilio.twiml.voice_response import VoiceResponse, Gather
3
4app = Flask(__name__)
5
6
7@app.route("/voice", methods=['GET', 'POST'])
8def voice():
9    """Respond to incoming phone calls with a menu of options"""
10    # Start our TwiML response
11    resp = VoiceResponse()
12
13    # Start our  verb
14    gather = Gather(num_digits=1)
15    gather.say('For sales, press 1. For support, press 2.')
16    resp.append(gather)
17
18    # If the user doesn't select an option, redirect them into a loop
19    resp.redirect('/voice')
20
21    return str(resp)
22
23if __name__ == "__main__":
24    app.run(debug=True)

If the user doesn't enter any input after a configurable timeout, Twilio will continue processing the TwiML in the document to determine what should happen next in the call. When the end of the document is reached, Twilio will hang up the call. In the above example, we use the verb to have Twilio request the same URL again, repeating the prompt for the user

If a user were to enter input with the example above, the user would hear the same prompt over and over again regardless of what button you pressed. By default, if the user does enter input in the , Twilio will send another HTTP request to the current webhook URL with a POST parameter containing the Digits entered by the user. In the sample above, we weren't handling this input at all. Let's update that logic to also process user input if it is present.

Branch your call logic based on the digits sent by the user

1from flask import Flask, request
2from twilio.twiml.voice_response import VoiceResponse, Gather
3
4app = Flask(__name__)
5
6
7@app.route("/voice", methods=['GET', 'POST'])
8def voice():
9    """Respond to incoming phone calls with a menu of options"""
10    # Start our TwiML response
11    resp = VoiceResponse()
12
13    # If Twilio's request to our app included already gathered digits,
14    # process them
15    if 'Digits' in request.values:
16        # Get which digit the caller chose
17        choice = request.values['Digits']
18
19        #  a different message depending on the caller's choice
20        if choice == '1':
21            resp.say('You selected sales. Good for you!')
22            return str(resp)
23        elif choice == '2':
24            resp.say('You need support. We will help!')
25            return str(resp)
26        else:
27            # If the caller didn't choose 1 or 2, apologize and ask them again
28            resp.say("Sorry, I don't understand that choice.")
29
30    # Start our  verb
31    gather = Gather(num_digits=1)
32    gather.say('For sales, press 1. For support, press 2.')
33    resp.append(gather)
34
35    # If the user doesn't select an option, redirect them into a loop
36    resp.redirect('/voice')
37
38    return str(resp)
39
40if __name__ == "__main__":
41    app.run(debug=True)

Specify an action to take after user input is collected

You may want to have an entirely different endpoint in your application handle the processing of user input. This is possible using the "action" attribute of the verb. Let's update our example to add a second endpoint that will be responsible for handling user input.

Add another route to handle the input from the user

1from flask import Flask, request
2from twilio.twiml.voice_response import VoiceResponse, Gather
3
4app = Flask(__name__)
5
6
7@app.route("/voice", methods=['GET', 'POST'])
8def voice():
9    """Respond to incoming phone calls with a menu of options"""
10    # Start our TwiML response
11    resp = VoiceResponse()
12
13    # Start our  verb
14    gather = Gather(num_digits=1, action='/gather')
15    gather.say('For sales, press 1. For support, press 2.')
16    resp.append(gather)
17
18    # If the user doesn't select an option, redirect them into a loop
19    resp.redirect('/voice')
20
21    return str(resp)
22
23
24@app.route('/gather', methods=['GET', 'POST'])
25def gather():
26    """Processes results from the  prompt in /voice"""
27    # Start our TwiML response
28    resp = VoiceResponse()
29
30    # If Twilio's request to our app included already gathered digits,
31    # process them
32    if 'Digits' in request.values:
33        # Get which digit the caller chose
34        choice = request.values['Digits']
35
36        #  a different message depending on the caller's choice
37        if choice == '1':
38            resp.say('You selected sales. Good for you!')
39            return str(resp)
40        elif choice == '2':
41            resp.say('You need support. We will help!')
42            return str(resp)
43        else:
44            # If the caller didn't choose 1 or 2, apologize and ask them again
45            resp.say("Sorry, I don't understand that choice.")
46
47    # If the user didn't choose 1 or 2 (or anything), send them back to /voice
48    resp.redirect('/voice')
49
50    return str(resp)
51
52if __name__ == "__main__":
53    app.run(debug=True)

The action attribute takes a relative URL which would point to another route your server is capable of handling. Now, instead of conditional logic in a single route, we use actions and redirects to handle our call logic with separate code paths.

Where to next?

If you're building call center type applications in Python, you might enjoy our IVR Phone Tree (Flask) tutorial, which implements a full sample application using these techniques.