Set up your Python and Flask development environment

This tutorial requires the following tools and understanding:

• Administrative access to your computer to install software
• A stable internet connection for downloading packages and dependencies
• Basic familiarity with using the command line or terminal
• A Twilio account (free tier available)
• A Twilio phone number (free trial numbers available)
• Python 3.9 or later
• ngrok

Consult the README for the latest supported Python version.

To check your Python version, open a terminal and run:

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$ python --version
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Python 3.9.0

On some systems, you might need to use python3 instead of python:

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$ python3 --version
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Python 3.11.5

Before you can start your Python project, you'll need an editor or integrated development environment (IDE) to write your code.

If you already have a code-writing tool of choice, you can use it for developing your Python application. If you're looking for something new, you might consider trying out a few options:

• Visual Studio Code is another text editor that's free, easy to set up, and available on all platforms.
• PyCharm is a fully integrated development environment (IDE) for Python. It takes longer to set up but comes with more helpful tools already installed.
• Vim is a perennial favorite text editor among advanced users.

If you're new to programming, consider giving Sublime Text and PyCharm a try before you settle on your favorite.

Virtual environments are useful because they keep each Python project's packages separate. This helps avoid problems when different projects need different versions of the same package. It also makes your code more reliable when developing and deploying. Follow these steps to create and activate a virtual environment:

1. Create the venv module from the standard library.

2. Use the appropriate command to create a new virtual environment named myproject. On some systems, you might need to use python3 instead of python:

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   # Python 3.7+ (using python or python3 depending on your system)
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   $ python -m venv myproject
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   # Or
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   $ python3 -m venv myproject

3. Activate the virtual environment using the following commands, depending on your operating system:

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   # Activate the virtual environment (macOS and Linux)
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   $ source myproject/bin/activate
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   # Activate the virtual environment (Windows)
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   $ myproject\Scripts\activate

You're almost ready to start writing your Flask web application. First, you need to install the Flask library and the Twilio Python SDK in your virtual environment.

1. Ensure your virtual environment is active.

2. Install Flask and the Twilio library using pip:

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   $ pip install Flask-Twilio

   Note: If you're using Python 3 outside of a virtual environment, you might need to use pip3 instead of pip.

3. After installing your dependencies, you might want to keep track of and control which versions you're using. Pip allows you to "freeze" your dependencies and record the versions in a file called requirements.txt. Create a requirements file with this command:

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   $ pip freeze > requirements.txt

You can test that your development environment is configured correctly by creating a simple Flask application. Follow these steps:

1. Create a new file named app.py and copy the following code into it:

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   from flask import Flask
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   app = Flask(__name__)
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   @app.route("/")
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   def hello():
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       return "Hello World!"
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   if __name__ == "__main__":
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       app.run()

2. Run your new Flask application with the command:

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   cd myproject
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   $ python app.py

   Note: On macOS and some Linux systems, you might need to use python3 instead of python:

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   cd myproject
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   $ python3 app.py

3. Open http://localhost:5000 in your browser. This will display the "Hello World!" response.

Most Twilio services use webhooks to communicate with your application. When Twilio receives an incoming phone call, for example, it reaches out to a URL in your application for instructions on how to handle the call.

Note: If you're using a virtual machine for your development environment, such as Vagrant, you might not be able to see your Flask application at the localhost hostname. Continue to the ngrok section for an easy way to fix this.

When you're building your Flask app locally, it's only accessible from your own computer. That means Twilio can't reach it from the internet to send requests or data.

ngrok is a helpful tool to solve this problem. Once started, it provides a unique URL on the ngrok.io domain which will forward incoming requests to your local development environment.

Once downloaded, make sure your Flask application is running, and then start ngrok using this command:

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ngrok http 5000
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Output resembles the following:
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```bash
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ngrok by @inconshreveable
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Tunnel Status  online
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Version        3.x.x
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Region         us
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Web Interface  http://127.0.0.1:4040
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Forwarding     http://<random_subdomain>.ngrok.io -> http://localhost:5000
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Forwarding     http://<random_subdomain>.ngrok.io -> http://localhost:5000
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Connections    ttl     opn     rt1     rt5     p50     p90
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               0       0       0.00    0.00    0.00    0.00

You should see a "Forwarding" line in your ngrok terminal output, e.g.:

Forwarding http://<random_subdomain>.ngrok.io -> http://localhost:5000

Look at the "Forwarding" line to see your unique ngrok domain name (for example, aaf29606.ngrok.io), and then open that URL in your browser.

If everything's working correctly, your Flask application's "Hello World!" message will be displayed at your new ngrok URL.

Anytime you're working on your Twilio application and need a URL for a webhook, ngrok will be needed to get a publicly accessible URL like this one.

You've learned about ngrok, pip, and virtual environments, and now you're ready to build your Flask application. Learn more with the following resources:

• SMS developer quickstart
• WhatsApp Business Platform with Twilio quickstart
• Programmable Voice quickstart
• Email API Quickstart for Python

• Flask documentation
• Full Stack Python - Flask