Environment variables usage in Python - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this environment variable read?

Consider this Python code that reads an environment variable named MY_VAR:

import os
os.environ['MY_VAR'] = 'hello'
value = os.getenv('MY_VAR')
print(value)

What will this code print?

Python

import os
os.environ['MY_VAR'] = 'hello'
value = os.getenv('MY_VAR')
print(value)

A None

B hello

C '' (empty string)

D KeyError

💡 Hint

Remember that os.getenv returns the value of the environment variable if it exists.

The code sets the environment variable MY_VAR to 'hello'. Then os.getenv('MY_VAR') reads it and returns 'hello'. So the print outputs 'hello'.

❓ Predict Output

intermediate

What does this code print when variable is missing?

Given this code snippet:

import os
value = os.getenv('NOT_SET', 'default')
print(value)

What will be printed if the environment variable NOT_SET is not defined?

Python

import os
value = os.getenv('NOT_SET', 'default')
print(value)

A KeyError

B None

C '' (empty string)

D default

💡 Hint

Check what the second argument to os.getenv does.

The second argument to os.getenv is the default value returned if the environment variable is not set. So it prints 'default'.

❓ Predict Output

advanced

What error does this code raise?

Look at this code:

import os
value = os.environ['MISSING_VAR']
print(value)

What happens if MISSING_VAR is not set in the environment?

Python

import os
value = os.environ['MISSING_VAR']
print(value)

A KeyError

B None

C '' (empty string)

D AttributeError

💡 Hint

Accessing environment variables via os.environ like a dictionary raises an error if the key is missing.

Accessing os.environ['MISSING_VAR'] raises a KeyError if the variable is not set.

❓ Predict Output

advanced

What is the output of this environment variable update?

Consider this code:

import os
os.environ['TEST_VAR'] = '123'
os.environ['TEST_VAR'] = '456'
print(os.getenv('TEST_VAR'))

What will be printed?

Python

import os
os.environ['TEST_VAR'] = '123'
os.environ['TEST_VAR'] = '456'
print(os.getenv('TEST_VAR'))

A 456

B None

C 123

D KeyError

💡 Hint

Think about what happens when you assign a new value to the same environment variable key.

The second assignment overwrites the first. So TEST_VAR becomes '456'. The print outputs '456'.

🧠 Conceptual

expert

Which option correctly explains environment variable visibility?

Which statement about environment variables in Python is true?

A Environment variables are shared across all running Python processes automatically.

B Changes to <code>os.environ</code> in a Python script affect the parent process environment.

C Environment variables set in a Python script are visible to child processes spawned after the change.

D Environment variables can be set permanently for all future Python scripts by modifying <code>os.environ</code>.

💡 Hint

Think about how environment variables propagate between processes.

Modifying os.environ affects only the current process and its child processes spawned after the change. It does not affect the parent or other running processes.