Install Flask in Python

Requirements

• Python 3 installed.
• The latest pip.
• python3-venv to make isolated Python environments.

Step 1: Install the venv tools

sudo apt install python3-venv

Step 2: Create a virtual environment

Make a folder for your project and a virtual environment in it:

mkdir myflaskapp
cd myflaskapp
python3 -m venv venv

(You can also use virtualenv venv if the virtualenv tool is installed.)

Step 3: Activate the environment

source ./venv/bin/activate

The prompt now starts with (venv).

Step 4: Check pip

pip -V

Step 5: Install Flask

pip install flask

Step 6: Check Flask

Open Python and import it:

python

import flask

If no error shows, Flask is installed. Leave Python with exit().

A first app

Create app.py:

from flask import Flask

app = Flask(__name__)

@app.route("/")
def home():
    return "Hello from Flask!"

Run it:

flask --app app run

Open http://127.0.0.1:5000.

To leave the virtual environment, type deactivate.

Quick recap

• Use a virtual environment for each project.
• pip install flask.
• Run with flask --app app run.