Add dotenv example

Author: gjbex

source-code/enviroment-variables/README.md

@@ -1,13 +1,17 @@
 # Environment variables
 
-This directory shows some examples of how to use environment variables in a Python
-script.
+This directory shows some examples of how to use environment variables in a
+Python script.
+
 
 ## What is it?
 
-1. `accumulate_data.py`: script that will read all `.txt` files in a directory defined
-  in an environment variable `DATA_DIR`.
+1. `accumulate_data.py`: script that will read all `.txt` files in a directory
+   defined in an environment variable `DATA_DIR`.
 1. `data`: directory that contains two text files with data.
+1. `dotenv`: the `dotenv` package is used to load environment variables from a
+   `.env` file.
+
 
 ## How to use it?
 

source-code/enviroment-variables/dotenv/.gitignore

@@ -0,0 +1,2 @@
+# include .env file to prevent sensitive data from being committed
+.env

source-code/enviroment-variables/dotenv/README.md

@@ -0,0 +1,17 @@
+# dotenv
+
+The `dotenv` package is a simple and efficient way to load environment
+variables from a `.env` file into your application's environment. It is
+commonly used in development and testing environments to manage configuration
+settings without hardcoding them into the source code.  Another important use
+case is to keep sensitive information, such as API keys and database
+credentials, out of version control systems.
+
+
+## What is it?
+
+1. `dot_env`: file to be renamed to `.env` in the directory where the script is
+   run.
+1. `dotenv_demo.py`: demo script that uses `dotenv` to load environment
+   variables from the `.env` file.
+1. `.gitignore`: to ignore the `.env` file in version control.

source-code/enviroment-variables/dotenv/dot_env

@@ -0,0 +1,2 @@
+MY_SECRET="if you see this, expect black helicopters"
+MY_PATH="somewhere/to/go"

source-code/enviroment-variables/dotenv/dotenv_demo.py

@@ -0,0 +1,26 @@
+#!/usr/bin/env python3
+
+from dotenv import load_dotenv
+import os
+
+
+def main():
+    # Check whether the environment variable is already set
+    if 'MY_SECRET' in os.environ:
+        print('MY_SECRET is already set in the environment.')
+    else:
+        # Load environment variables from .env file
+        print('Loading environment variables from .env file...')
+        load_dotenv()
+
+    # Access an environment variable
+    secret_key = os.getenv('MY_SECRET')
+
+    if secret_key:
+        print(f'MY_SECRET_KEY: {secret_key}')
+    else:
+        print('MY_SECRET not found in environment variables.')
+
+
+if __name__ == '__main__':
+    main()