How To Install Flask

Introduction

Flask is one of the most popular web application frameworks written in Python. It is a microframework designed for an easy and quick start. Extending with tools and libraries adds more functionality to Flask for more complex projects.

This article explains how to install Flask in a virtual testing environment and create a simple Flask application.

Prerequisites

• Installed Python 2.7 or Python 3.5 and newer
• CLI with administrator privileges

Step 1: Install Virtual Environment

Install Flask in a virtual environment to avoid problems with conflicting libraries. Check Python version before starting:

• Python 3 comes with a virtual environment module called venv preinstalled. If you have Python 3 installed, skip to Step 2.
• Python 2 users must install the virtualenv module. If you have Python 2, follow the instructions outlined in Step 1.

Install virtualenv on Linux

The package managers on Linux provides virtualenv.

• For Debian/Ubuntu:

1. Start by opening the Linux terminal.

2. Use apt to install virtualenv on Debian, Ubuntu and other related distributions:

sudo apt install python-virtualenv

• For CentOS/Fedora/Red Hat:

1. Open the Linux terminal.

2. Use yum to install virtualenv on CentOS, Red Hat, Fedora and related distributions:

sudo yum install python-virtualenv

Install virtualenv on MacOS

1. Open the terminal.

2. Install virtualenv on Mac using pip:

sudo python2 -m pip install virtualenv

Install virtualenv on Windows

1. Open the command line with administrator privileges.

2. Use pip to install virtualenv on Windows:

py -2 -m pip install virtualenv

Step 2: Create an Environment

1. Make a separate directory for your project:

mkdir <project name>

2. Move into the directory:

cd <project name>

3. Within the directory, create the virtual environment for Flask. When you create the environment, a new folder appears in your project directory with the environment’s name.

Create an Environment in Linux and MacOS

• For Python 3:

To create a virtual environment for Python 3, use the venv module and give it a name:

python3 -m venv <name of environment>

• For Python 2:

For Python 2, use the virtualenv module to create a virtual environment and name it:

python -m virtualenv <name of environment>

Listing the directory structure with the ls command shows the newly created environment:

Create an Environment in Windows

• For Python 3:

Create and name a virtual environment in Python 3 with:

py -3 -m venv <name of environment>

• For Python 2:

For Python 2, create the virtual environment with the virtualenv module:

py -2 -m virtualenv <name of environment>

List the folder structure using the dir command:

dir *<project name>*

The project directory shows the newly created environment:

Step 3: Activate the Environment

Activate the virtual environment before installing Flask. The name of the activated environment shows up in the CLI after activation.

Activate the Environment on Linux and MacOS

Activate the virtual environment in Linux and MacOS with:

. <name of environment>/bin/activate

Activate the Environment on Windows

For Windows, activate the virtual environment with:

<name of environment>\Scripts\activate

Step 4: Install Flask

Install Flask within the activated environment using pip:

pip install Flask

Flask is installed automatically with all the dependencies.

Step 5: Test the Development Environment

1. Create a simple Flask application to test the newly created development environment.

2. Make a file in the Flask project folder called hello.py.

3. Edit the file using a text editor and add the following code to make an application that prints "Hello world!":

from flask import Flask
app = Flask(__name__)
@app.route('/')
def hello_world():
    return 'Hello world!'

4. Save the file and close.

5. Using the console, navigate to the project folder using the cd command.

6. Set the FLASK_APP environment variable.

• For Linux and Mac:

export FLASK_APP=hello.py

• For Windows:

setx FLASK_APP "hello.py"

7. Run the Flask application with:

flask run

The output prints out a confirmation message and the address.

8. Copy and paste the address into the browser to see the project running:

Conclusion

Flask web applications are easy to configure and run. It is one of the most popular web application frameworks for Python.

Read about the best Python IDEs and code editors to choose the best environment for further web development with Flask.