Building a Python Bot for Facebook Messenger

Introduction
Prerequisites
Setup
Creating a Facebook Page and App
Installing Dependencies
Coding the Python Bot
Testing the Bot
Conclusion

Introduction

In this tutorial, we will learn how to build a Python bot for Facebook Messenger. We will utilize the Facebook Messenger API and the Flask framework to create a bot that can receive messages from users and reply to them.

By the end of this tutorial, you will have a working Python bot that can interact with users on Facebook Messenger.

Prerequisites

Before starting this tutorial, make sure you have the following prerequisites:

Basic knowledge of Python programming
Understanding of HTTP requests and responses
A Facebook account

Setup

To get started, let’s set up the necessary components for building our bot.

Creating a Facebook Page and App

Log in to your Facebook account.
Go to Facebook for Developers.
Create a new Facebook app by clicking on the “My Apps” dropdown and selecting “Create App.”
Choose a display name for your app and specify the purpose.
Navigate to the “Messenger” settings for your app.
Enable the webhook option and subscribe to the “messages” event.
Generate a page access token and copy it for later use.
Create a Facebook page if you don’t have one already.
Link your Facebook app to the page by going to the “Page Access Token” section and associating the app with the page.

Installing Dependencies

Now, let’s install the required dependencies for our Python bot. Open your terminal or command prompt and follow these steps:

Create a new directory for your project:

mkdir python-messenger-bot
cd python-messenger-bot

Set up a virtual environment to keep your project dependencies isolated:
```
python3 -m venv env
source env/bin/activate
```
Install the necessary Python packages:
```
pip install flask requests
```
Coding the Python Bot

Now that we have everything set up, let’s start coding our Python bot.

Create a new Python file, app.py, in your project directory.

Import the required modules:

from flask import Flask, request
import requests

Create a Flask application instance:
```
app = Flask(__name__)
```

Create the webhook endpoint for receiving messages:

@app.route('/webhook', methods=['GET', 'POST'])
def webhook():
    if request.method == 'GET':
        verify_token = request.args.get('hub.verify_token')
        if verify_token == 'YOUR_VERIFY_TOKEN':
            return request.args.get('hub.challenge')
        return 'Invalid Verification Token'

    elif request.method == 'POST':
        data = request.get_json()

        if data['object'] == 'page':
            for entry in data['entry']:
                for messaging_event in entry['messaging']:
                    sender_id = messaging_event['sender']['id']
                    message_text = messaging_event['message']['text']

                    # Process the message and send a reply
                    send_message(sender_id, message_text)

            return 'OK'
           
        return 'Not a Page Event'

    return 'Invalid Request'

Add a function to send messages back to the user:

def send_message(sender_id, message_text):
    # Prepare the data for the API request
    headers = {'Content-Type': 'application/json'}
    params = {
        'access_token': 'YOUR_PAGE_ACCESS_TOKEN'
    }
    data = {
        'recipient': {
            'id': sender_id
        },
        'message': {
            'text': message_text
        }
    }

    # Send the message using the Facebook Messenger API
    response = requests.post(
        'https://graph.facebook.com/v13.0/me/messages',
        headers=headers,
        params=params,
        json=data
    )

    if response.status_code != 200:
        print('Failed to send message:', response.json())

Run the Flask application:

if __name__ == '__main__':
    app.run()

Replace 'YOUR_VERIFY_TOKEN' in the webhook() function with your own custom verification token.
Replace 'YOUR_PAGE_ACCESS_TOKEN' in the send_message() function with the page access token you generated earlier.

Testing the Bot

To test the bot, follow these steps:

Start the Flask application by running python app.py in your terminal.
Use a tool like Ngrok to expose your local development server to the internet.
In the Facebook for Developers dashboard, set the “Webhook URL” to the Ngrok URL followed by /webhook (e.g., https://randomstring.ngrok.io/webhook).
Save the changes and make sure the webhook is properly verified.
Go to your Facebook page and send a message to your bot.
Verify that the bot replies to your message correctly.

Conclusion

In this tutorial, we have learned how to build a Python bot for Facebook Messenger using the Facebook Messenger API and the Flask framework. We started by setting up a Facebook page and app, followed by installing the necessary dependencies. Then, we coded a webhook endpoint to receive messages and send replies to users.

You can now enhance your bot by adding more capabilities, such as handling different types of messages, integrating with external APIs, or implementing natural language processing. Be sure to refer to the Facebook Messenger API documentation for more advanced features and functionalities.

Happy bot building!

Published: 6 November 2022