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Set up your Python and Flask development environment


In this guide, you'll set up your Python and Flask development environment to build Twilio applications.


Set up Python

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Consult the README(link takes you to an external page) 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
(information)

Info

On macOS, the python command might refer to Python 2, and python3 refers to Python 3. Use python3 when working with Python 3 on macOS.


How you install Python varies depending on your operating system.

Operating systemInstructions
macOSmacOS comes with Python pre-installed, but it's recommended to install your own Python 3 version. Homebrew(link takes you to an external page) is a popular tool for installing Python 3 on macOS. You can find detailed instructions in the Python Guide for macOS(link takes you to an external page).
WindowsThe best way to install Python on Windows is by using the official installer from the Python Software Foundation(link takes you to an external page). The x86-64 (64-bit) version is generally recommended, but if you need better compatibility with certain third-party packages, the x86 (32-bit) version may be more suitable.
LinuxThe exact instructions to install Python vary by distribution. Find instructions for Unix(link takes you to an external page) on the official Python website, or check your distribution's documentation for details.

Install a text editor or IDE

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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:

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


Create and activate a virtual environment

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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

Install Flask and the Twilio Python SDK

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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:

    $ 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:

    $ pip freeze > requirements.txt

Create a simple Flask application

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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(link takes you to an external page) in your browser. You should see 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.

To start, head over to the ngrok download page and download the binary for your operating system: https://ngrok.com/download(link takes you to an external page).

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

$ ngrok http 5000

You should see output similar to this:

ngrok output showing a sample domain forwarding to localhost port 5000.

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

Forwarding http://aaf29606.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, you should see your Flask application's "Hello World!" message displayed at your new ngrok URL.

Anytime you're working on your Twilio application and need a URL for a webhook, you should use ngrok 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:

Twilio

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