Setting Flask environment variables

You can pass some settings into your buggy editor (which is a Flask app) using environment variables. The most immediately useful one of these is

FLASK_ENV

which ideally should have the value development while you are working on your project.

Environment variables are a feature of the operating system, not Python, so how you set them differs depending on what platform you are on.

You can check if your setting of FLASK_ENV has worked by looking at the output of your webserver when you run it (with your Python command). You should see:

* Environment: development

On Windows

Use the Registry

You can set environment variables in the registry. Find the System Properties dialog in the Windows Control Panel. There's an Environment Variables button there. Good luck.

With Powershell

If you do this:

set FLASK_ENV=development

That should set FLASK_ENV for the remainder of the session. When you run py app.py or python3 app.py (depending on what python command you're using it) should pick it up.

With Git bash

Git bash on Windows mimics the way things work in Unix, so follow the Unix instructions below.

On Unix/Mac

Use export to set the variable:

export FLASK_ENV=development

That should set FLASK_ENV for the remainder of the session. When you run python3 app.py it should pick it up.

Alternatively, you can set the variable as you launch the command. This method is popular because it's explicit:

FLASK_ENV=development python3 app.py

Any platform:

Tell Python to load it from .env

This is a nice solution because it works on all the platforms and if you do it once, it sticks until you delete the .env file.

If you are using a virtual environment, make sure you've activated it before you attempt to install the dotenv module (because you want pip to install the new module in that environment).

Install the dotenv module by doing:

pip install python-dotenv

If you can't get pip to work (maybe "no such command") you can try this instead (again use python3 or py depending on what you Python command is):

python3 -m pip install python-dotenv

Once dotenv is installed, when Flask runs it will notice if there's a file called .env where you are, and if there is, will load any environment variables declared inside it.

So make a file called .env. This can be tricky on Windows because most editors try to add .txt to the end. If you use Windows explorer and you do not have "show extensions" enabled (so you see app instead of app.txt) change that because in CompSci you need to know the real names of the files you're working with.

Edit .env so it contains this line:

FLASK_ENV=development

And you're done. Now when you run your app, it should automatically pick up any environment variable settings that are in that file.