What is the use of python-dotenv?

From the Github page:

Reads the key,value pair from .env and adds them to environment variable. It is great of managing app settings during development and in production using 12-factor principles.

Assuming you have created the .env file along-side your settings module.

.
├── .env
└── settings.py

Add the following code to your settings.py

# settings.py
import os
from os.path import join, dirname
from dotenv import load_dotenv

dotenv_path = join(dirname(__file__), '.env')
load_dotenv(dotenv_path)

SECRET_KEY = os.environ.get("SECRET_KEY")
DATABASE_PASSWORD = os.environ.get("DATABASE_PASSWORD")

.env is a simple text file. With each environment variables listed per line, in the format of KEY=”Value”, lines starting with # is ignored.

SOME_VAR=someval
# I am a comment and that is OK
FOO="BAR"