Environment variable management in Flask - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

How does Flask access environment variables in this code?

Consider this Flask app snippet that reads an environment variable to configure debug mode:

import os
from flask import Flask

app = Flask(__name__)
app.config['DEBUG'] = os.getenv('FLASK_DEBUG', 'False') == 'True'

@app.route('/')
def home():
    return 'Debug is ' + str(app.config['DEBUG'])

What will be the output if the environment variable FLASK_DEBUG is set to True?

Flask

import os
from flask import Flask

app = Flask(__name__)
app.config['DEBUG'] = os.getenv('FLASK_DEBUG', 'False') == 'True'

@app.route('/')
def home():
    return 'Debug is ' + str(app.config['DEBUG'])

A Debug is True

B Debug is False

C Debug is None

D Debug is 'True'

💡 Hint

Remember that environment variables are strings and the code compares the string value.

The environment variable FLASK_DEBUG is read as a string. The code compares it to the string 'True'. If it matches, app.config['DEBUG'] becomes True (boolean). So the output shows Debug is True.

📝 Syntax

intermediate

Which option correctly loads environment variables from a .env file in Flask?

You want to load environment variables from a .env file in your Flask app. Which code snippet correctly does this using python-dotenv?

A

from dotenv import load_dotenv
load_dotenv()

app = Flask(__name__)

B

import dotenv
dotenv.load()

app = Flask(__name__)

C

from flask_dotenv import load_dotenv
load_dotenv()

app = Flask(__name__)

D

import os
os.load_dotenv()

app = Flask(__name__)

💡 Hint

Check the official python-dotenv package usage.

The correct way to load environment variables from a .env file is to use from dotenv import load_dotenv and then call load_dotenv(). Other options either use wrong module names or functions that don't exist.

🔧 Debug

advanced

Why does this Flask app fail to read updated environment variables after .env change?

Given this Flask app code:

from dotenv import load_dotenv
import os
from flask import Flask

load_dotenv()
app = Flask(__name__)

@app.route('/')
def index():
    return os.getenv('MY_VAR', 'Not Set')

You update the .env file to change MY_VAR but the app still returns the old value without restarting. Why?

Flask

from dotenv import load_dotenv
import os
from flask import Flask

load_dotenv()
app = Flask(__name__)

@app.route('/')
def index():
    return os.getenv('MY_VAR', 'Not Set')

A The load_dotenv() function does not read .env files automatically.

B Flask blocks environment variable access inside route functions.

C os.getenv caches values and does not reflect changes until Python interpreter restarts.

D Environment variables are loaded once at startup; changes in .env require app restart to reload.

💡 Hint

Think about when environment variables are loaded and how Flask apps run.

Environment variables loaded by load_dotenv() happen once when the app starts. If you change the .env file later, the app does not reload those variables automatically. You must restart the app to see changes.

❓ state_output

advanced

What is the value of app.config['SECRET_KEY'] after this code runs?

Consider this Flask app snippet:

import os
from flask import Flask

os.environ['SECRET_KEY'] = 'supersecret'
app = Flask(__name__)
app.config['SECRET_KEY'] = os.getenv('SECRET_KEY', 'defaultkey')

What is the value of app.config['SECRET_KEY']?

Flask

import os
from flask import Flask

os.environ['SECRET_KEY'] = 'supersecret'
app = Flask(__name__)
app.config['SECRET_KEY'] = os.getenv('SECRET_KEY', 'defaultkey')

A None

B defaultkey

C supersecret

D Raises KeyError

💡 Hint

Remember how os.environ and os.getenv work.

The environment variable SECRET_KEY is set in os.environ before the Flask app reads it. So os.getenv('SECRET_KEY') returns 'supersecret'.

🧠 Conceptual

expert

Which approach best secures sensitive environment variables in Flask deployment?

You want to keep sensitive environment variables like SECRET_KEY safe in production. Which approach is best practice?

A Store sensitive variables in a .env file committed to version control for easy access.

B Set environment variables directly on the production server or container without committing to code.

C Hardcode sensitive values in the Flask app source code for simplicity.

D Use Flask's config.from_pyfile() with a config file containing secrets committed to repo.

💡 Hint

Think about security and version control exposure.

Best practice is to set sensitive environment variables directly on the production environment (server or container) so they are not stored in code or version control. This reduces risk of accidental exposure.