Environment variables usage in Python - Mini Project: Build & Apply

Environment variables usage

📖 Scenario: Imagine you are creating a simple program that needs to use a secret key to access a service. Instead of writing the secret key directly in your code, you will use environment variables to keep it safe and separate.

🎯 Goal: You will learn how to read environment variables in Python and use them in your program.

📋 What You'll Learn

Create an environment variable named SECRET_KEY with the value abc123 in your system before running the program.

Use the os module to access environment variables.

Store the environment variable value in a variable called secret_key.

Print the value of secret_key.

💡 Why This Matters

🌍 Real World

Environment variables are used to keep sensitive information like keys and passwords out of the code, making programs safer and easier to manage.

💼 Career

Many jobs require working with environment variables to configure applications securely, especially in web development and cloud computing.

1

Import the os module

Write import os to import the module needed to access environment variables.

Python

# Your code here

Hint

The os module helps you work with environment variables.

2

Read the environment variable

Create a variable called secret_key and set it to the value of the environment variable SECRET_KEY using os.getenv.

Python

import os
# Your code here

Hint

Use os.getenv('SECRET_KEY') to get the value of the environment variable.

3

Check if the environment variable is set

Write an if statement to check if secret_key is None. If it is, set secret_key to the string 'No key found'.

Python

import os
secret_key = os.getenv('SECRET_KEY')
# Your code here

Hint

This helps your program handle the case when the environment variable is not set.

4

Print the secret key

Write print(secret_key) to display the value of the secret_key variable.

Python

import os
secret_key = os.getenv('SECRET_KEY')
if secret_key is None:
    secret_key = 'No key found'
# Your code here

Hint

This will show the secret key if it is set, or the message if not.

Practice

1. What is the main purpose of using environment variables in a Python program?

easy

A. To print output on the screen

B. To write data to files

C. To create new Python functions

D. To store configuration settings outside the code

Solution

1. Step 1: Understand environment variables role

   Environment variables hold settings or secrets outside the program code.

2. Step 2: Identify correct purpose

   Using environment variables helps keep code flexible and secure by not hardcoding values.

3. Final Answer:

   To store configuration settings outside the code -> Option D

4. Quick Check:

   Environment variables = external settings [OK]

Hint: Environment variables hold settings outside code [OK]

Common Mistakes:

• Thinking environment variables store data inside the program
• Confusing environment variables with file operations
• Assuming environment variables create functions

2. Which of the following is the correct way to import the module needed to access environment variables in Python?

easy

A. import environment

B. import os

C. import sys

D. import env

Solution

1. Step 1: Recall Python module for environment variables

   The standard module to access environment variables is os.

2. Step 2: Check options for correct import

   Only import os is correct; others are invalid or unrelated.

3. Final Answer:

   import os -> Option B

4. Quick Check:

   Module for env vars = os [OK]

Hint: Use 'import os' to access environment variables [OK]

Common Mistakes:

• Using 'import environment' which does not exist
• Confusing 'sys' module with environment variables
• Trying to import 'env' which is not a standard module

3. What will be the output of this code if the environment variable USER is set to alice?

import os
name = os.getenv('USER', 'guest')
print(name)

medium

A. alice

B. USER

C. null

D. guest

Solution

1. Step 1: Understand os.getenv behavior

   os.getenv('USER', 'guest') returns the value of USER if set, else 'guest'.

2. Step 2: Apply given environment variable value

   Since USER is set to 'alice', the function returns 'alice'.

3. Final Answer:

   alice -> Option A

4. Quick Check:

   os.getenv returns env var value if set [OK]

Hint: os.getenv returns env var value or default [OK]

Common Mistakes:

• Assuming default is always returned
• Printing the variable name instead of its value
• Confusing null with default value

4. Identify the error in this code snippet that tries to read an environment variable:

import os
api_key = os.getenv('API_KEY')
print(api_key.upper())

Assume API_KEY is not set in the environment.

medium

A. AttributeError because api_key is null

B. SyntaxError due to missing parentheses

C. No error, code runs fine

D. NameError because os is not imported

Solution

1. Step 1: Check os.getenv return when variable missing

   When API_KEY is not set, os.getenv returns null.

2. Step 2: Understand method call on null

   Calling upper() on null causes an AttributeError because null has no such method.

3. Final Answer:

   AttributeError because api_key is null -> Option A

4. Quick Check:

   null.upper() causes AttributeError [OK]

Hint: Check for null before calling string methods [OK]

Common Mistakes:

• Assuming os.getenv returns empty string if missing
• Ignoring that null has no string methods
• Thinking code runs without error

5. You want to safely read an environment variable PORT as an integer with a default of 8080 if not set or invalid. Which code snippet correctly does this?

hard

A. port = int(os.getenv('PORT') or 8080)

B. port = os.getenv('PORT', 8080)

C. try:\n port = int(os.getenv('PORT'))\nexcept (TypeError, ValueError):\n port = 8080

D. port = int(os.getenv('PORT', 8080))

Solution

1. Step 1: Understand the problem requirements

   We must convert PORT to int, use 8080 if missing or invalid (non-integer).

2. Step 2: Analyze each option

   port = int(os.getenv('PORT', 8080)) fails if PORT is set but not an integer string (raises ValueError). port = os.getenv('PORT', 8080) does not convert to int. port = int(os.getenv('PORT') or 8080) uses or but fails if PORT is set to invalid string (ValueError). try:\n port = int(os.getenv('PORT'))\nexcept (TypeError, ValueError):\n port = 8080 uses try-except to handle missing or invalid values safely.

3. Final Answer:

   try:\n port = int(os.getenv('PORT'))\nexcept (TypeError, ValueError):\n port = 8080 -> Option C

4. Quick Check:

   Use try-except to safely convert env var [OK]

Hint: Use try-except to handle invalid env var conversions [OK]

Common Mistakes:

• Not handling invalid integer strings
• Assuming default works if env var is invalid
• Not converting string to int