How to set up your Python and Flask development environment

In this guide we’ll cover how to set up your Python development environment for a Flask project. We'll use virtual environments to isolate our dependencies, and pip for package management. Also, we'll talk about a couple helpful tools that we recommend for prototyping Python applications that use Twilio: ngrok and the Twilio Python SDK.

Let’s get started!

Choose a Python version

There are two different versions of Python in widespread use today: Python 2 and Python 3. If you’re new to Python, choosing the right version for your project can be confusing.

Python 3 was first released in 2008, but some parts of the Python community continue to prefer Python 2 for various reasons. You can read more about the history of Python 2 vs. Python 3 here.

Today almost all popular Python libraries support both versions, including Twilio’s Python SDK. We recommend starting new projects using Python 3 unless there is a specific library important to your project which is only compatible with Python 2.

# Check your Python version
$ python --version
Python 3.5.2

If Python is already installed on your system, you can check its version by running python --version.

Install Python

How you install Python varies depending on your operating system.

Operating System Instructions
OS X OS X already has Python installed, but we recommend configuring your own Python installation. Homebrew is our tool of choice for getting Python 2 or 3 installed on OS X. You can find detailed instructions here.
Windows The best way to install Python on Windows is using the official installer from the Python Software Foundation. The x86 (32-bit) version will tend to have better compatibility with third-party packages.
Linux The exact instructions to install Python vary by distribution. Find instructions for Ubuntu, CentOS, and other distributions here.

Install a text editor or IDE

Before we can start our Python project we’ll need something to write it with.

If you already have a code writing tool of choice, you can stick with it for developing your Python application. If you're looking for something new, we recommend trying out a few options: 

  • Sublime Text is a text editor popular for its ease of use and extensibility. Start here if you’re eager to get coding and don’t think you’ll want a lot of frills in your development environment.
  • PyCharm is a full Integrated Development Environment (IDE) for Python. It takes longer to set up but comes with more helpful tools already installed.
  • Python Tools for Visual Studio is a great option if you're already a Visual Studio user.
  • Vim is a perernnial favorite text editor among advanced users

If you’re new to programming, we recommend giving Sublime Text and PyCharm each a try before you settle on your favorite.

Start a new project with virtualenv

Before starting any new Python project we should create a virtual environment for it.

Virtual environments (shortened as "virtualenv") separate our new project’s Python dependencies from our other projects and from the Python libraries our operating system uses. If you don’t use a virtualenv, there’s a good chance you might break part of your OS.

Install this Python utility, which will allow you to create and manage Python virtual environments. Use the "virtualenv" command to create a new virtual environment, using its sole argument to name your new environment. The instructions to activate your new virtualenv vary by operating system:

# Create a new virtualenv named "myproject"
$ virtualenv myproject
New python executable in myproject/bin/python
Installing setuptools, pip, wheel...done.

# Activate the virtualenv (OS X & Linux)
$ source myproject/bin/activate

# Activate the virtualenv (Windows)
$ myproject\Scripts\activate

You’ll need to activate your virtual environment every time you work on your Python project. In the rare cases when you want to deactivate your virtualenv without closing your terminal session, just use the deactivate command.

Install Flask and the Twilio Python SDK

We’re almost ready to start writing our Flask web application, but first we need to install the Flask library in our virtual environment.

# Use pip to install the Flask and twilio libraries
$ pip install Flask twilio
Collecting Flask
  Using cached Flask-0.11.1-py2.py3-none-any.whl
Collecting twilio
Collecting click>=2.0 (from Flask)
Collecting itsdangerous>=0.21 (from Flask)
Collecting Werkzeug>=0.7 (from Flask)
  Using cached Werkzeug-0.11.11-py2.py3-none-any.whl
Collecting Jinja2>=2.4 (from Flask)
  Using cached Jinja2-2.8-py2.py3-none-any.whl
Collecting pytz (from twilio)
  Using cached pytz-2016.7-py2.py3-none-any.whl
Collecting six (from twilio)
  Using cached six-1.10.0-py2.py3-none-any.whl
Collecting httplib2>=0.7 (from twilio)
Collecting MarkupSafe (from Jinja2>=2.4->Flask)
Installing collected packages: click, itsdangerous, Werkzeug, MarkupSafe, Jinja2, Flask, pytz, six, httplib2, twilio
Successfully installed Flask-0.11.1 Jinja2-2.8 MarkupSafe-0.23 Werkzeug-0.11.11 click-6.6 httplib2-0.9.2 itsdangerous-0.24 pytz-2016.7 six-1.10.0 twilio-5.6.0

Python uses pip to manage dependencies, so the command to pull Flask and the Twilio SDK into our development environment is pip install Flask twilio.

After you get your dependencies installed and confirm they're doing the trick for you, you'll probably want to keep track of and control what versions of the dependencies you're using. Pip allows us to "freeze" our dependencies, and record which versions we are using in a file that (by convention) is called requirements.txt. Create a requirements file with this command:

pip freeze > requirements.txt

If later on you wish to install this same set of dependencies again, you can install them from this file with the following command:

pip install -r requirements.txt

Create a simple Flask application

We can test that our development environment is configured correctly by creating a simple Flask application. We’ll grab the nine-line example from Flask’s homepage and drop it in a new file called `app.py`.

from flask import Flask
app = Flask(__name__)

@app.route("/")
def hello():
    return "Hello World!"

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

We can then try running our new Flask application with the command python app.py. You can then open http://localhost:5000 in your browser and you should see the “Hello World!” response.

Note: If you’re using a virtual machine for your development environment, like vagrant, you might not be able to see your Flask application at the localhost host name. Continue on to the ngrok section for an easy way to fix this.

Install ngrok

Once you see your sample Flask application’s “Hello World!” message, your development environment is ready to go. But for most Twilio projects you’ll want to install one more helpful tool: ngrok.

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.

When you’re working on your Flask application in your development environment, your app is only reachable by other programs on the same computer, so Twilio won’t be able to talk to it.

Ngrok is our favorite tool for solving 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 grab the binary for your operating system: https://ngrok.com/download

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 screen

Look at the “Forwarding” line to see your unique Ngrok domain name (ours is "aaf29606.ngrok.io") and then point your browser at that domain name.

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.

Where to next?

Nicely done! You've learned about ngrok, pip and virtual environments, and you’re now ready to build out your Flask application.

Ready to build something more substantiate with Twilio? Here are a few other resources we like:

Twilio

Flask

Andrew Baker
Paul Kamp
Kevin Whinnery
David Prothero

Need some help?

We all do sometimes; code is hard. Get help now from our support team, or lean on the wisdom of the crowd browsing the Twilio tag on Stack Overflow.