Configuration management in Flask - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to load configuration from a Python file in Flask.

Flask

app = Flask(__name__)
app.config.from_pyfile([1])

Drag options to blanks, or click blank then click option'

A'config.json'

Bconfig

C'config.py'

Dconfig.py

Attempts:

3 left

💡 Hint

Common Mistakes

Passing the filename without quotes causes an error.

Using a JSON file with from_pyfile does not work.

Flask's from_pyfile method expects the filename as a string, so you must pass the filename in quotes.

2fill in blank

medium

Complete the code to set a configuration value directly in Flask.

Flask

app = Flask(__name__)
app.config[[1]] = 'development'

Drag options to blanks, or click blank then click option'

A'ENV'

BENV

C'env'

Denvironment

Attempts:

3 left

💡 Hint

Common Mistakes

Using unquoted keys causes a NameError.

Using lowercase keys does not set the expected config.

Configuration keys must be strings, so use quotes around ENV.

3fill in blank

hard

Fix the error in loading configuration from an object in Flask.

Flask

class Config:
    DEBUG = True

app = Flask(__name__)
app.config.from_object([1])

Drag options to blanks, or click blank then click option'

AConfig()

BConfig

C'Config'

D'config.Config'

Attempts:

3 left

💡 Hint

Common Mistakes

Passing an instance causes an error.

Passing the class name as a string without module path fails if not imported.

The from_object method expects the class or its import path as a string, but passing the class itself (without parentheses) is correct.

4fill in blank

hard

Fill both blanks to create a config dictionary with only keys starting with 'MYAPP_'.

Flask

filtered_config = {k: v for k, v in app.config.items() if k.[1]('MYAPP_') and v [2] None}

Drag options to blanks, or click blank then click option'

Astartswith

Bis not

Cendswith

D==

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'endswith' instead of 'startswith' filters wrong keys.

Using '==' to check None causes errors.

Use startswith to check key prefix and is not to exclude None values.

5fill in blank

hard

Fill all three blanks to load config from environment variable and fallback to default.

Flask

import os

config_path = os.getenv([1], [2])
app.config.from_pyfile([3])

Drag options to blanks, or click blank then click option'

A'MYAPP_CONFIG'

B'default.cfg'

Cconfig_path

D'config.cfg'

Attempts:

3 left

💡 Hint

Common Mistakes

Passing the config filename directly instead of the variable.

Not providing a default fallback causes errors if env var missing.

Use os.getenv with the environment variable name and default file. Then load config from the resolved path.

Practice

1. What is the primary purpose of app.config in a Flask application?

easy

A. To define URL routes

B. To handle user sessions

C. To render HTML templates

D. To store and manage application settings

Solution

1. Step 1: Understand the role of app.config

   app.config is a special dictionary in Flask used to keep app settings organized.

2. Step 2: Compare with other Flask features

   User sessions, URL routes, and templates are handled by other parts of Flask, not app.config.

3. Final Answer:

   To store and manage application settings -> Option D

4. Quick Check:

   App settings = app.config [OK]

Hint: Remember: config means settings storage [OK]

Common Mistakes:

• Confusing config with routing or templates
• Thinking config handles user data
• Assuming config runs code

2. Which of the following is the correct way to set a configuration value named DEBUG to True in Flask?

easy

A. app.config['DEBUG'] = True

B. app.config.DEBUG = True

C. app.set_config('DEBUG', True)

D. app.config.set('DEBUG', True)

Solution

1. Step 1: Recall Flask config syntax

   Flask config uses dictionary syntax: app.config['KEY'] = value.

2. Step 2: Check each option

   app.config['DEBUG'] = True uses correct dictionary syntax. Dot notation, set_config, and config.set use invalid or non-existent methods.

3. Final Answer:

   app.config['DEBUG'] = True -> Option A

4. Quick Check:

   Set config like dict key-value [OK]

Hint: Use square brackets to set config keys [OK]

Common Mistakes:

• Using dot notation instead of dictionary syntax
• Calling non-existent methods like set_config
• Confusing config with other Flask methods

3. Given this Flask code snippet:

app = Flask(__name__)
app.config['DEBUG'] = False
app.config.from_mapping({'DEBUG': True, 'TESTING': True})
print(app.config['DEBUG'])

What will be printed?

medium

A. False

B. True

C. None

D. KeyError

Solution

1. Step 1: Understand config assignment order

   First, DEBUG is set to False. Then from_mapping updates it to True.

2. Step 2: Determine final value

   The last assignment wins, so DEBUG becomes True.

3. Final Answer:

   True -> Option B

4. Quick Check:

   Last config set wins [OK]

Hint: Later config calls overwrite earlier ones [OK]

Common Mistakes:

• Assuming first value stays
• Thinking from_mapping adds without overwrite
• Expecting error on duplicate keys

4. What is wrong with this Flask configuration code?

app = Flask(__name__)
app.config.from_pyfile('config.py')
app.config['SECRET_KEY'] = 'mysecret'

Assuming config.py does not exist in the project folder.

medium

A. It will raise a FileNotFoundError

B. It will silently ignore missing file

C. It will set SECRET_KEY before loading file

D. It will overwrite SECRET_KEY with None

Solution

1. Step 1: Understand from_pyfile behavior

   from_pyfile tries to load a Python file and raises an error if missing.

2. Step 2: Check file existence

   Since config.py does not exist, a FileNotFoundError occurs immediately.

3. Final Answer:

   It will raise a FileNotFoundError -> Option A

4. Quick Check:

   Missing config file causes error [OK]

Hint: Missing config files cause errors, not silent skips [OK]

Common Mistakes:

• Thinking Flask ignores missing config files
• Assuming config keys set before loading file are overwritten
• Expecting None values on missing keys

5. You want to load configuration in Flask from environment variables but provide default values if they are missing. Which code snippet correctly achieves this?

hard

A. app.config['DEBUG'] = os.environ['DEBUG'] or False

B. app.config['DEBUG'] = os.getenv('DEBUG') or None

C. app.config['DEBUG'] = os.getenv('DEBUG', False)

D. app.config['DEBUG'] = os.environ.get('DEBUG')

Solution

1. Step 1: Understand environment variable access

   os.getenv('KEY', default) returns the environment value or default if missing.

2. Step 2: Analyze each option

   app.config['DEBUG'] = os.getenv('DEBUG', False) uses os.getenv with default False, correctly providing fallback. app.config['DEBUG'] = os.environ['DEBUG'] or False may raise KeyError if 'DEBUG' missing. app.config['DEBUG'] = os.environ.get('DEBUG') returns None if missing but no default. app.config['DEBUG'] = os.getenv('DEBUG') or None returns None if missing, not False.

3. Final Answer:

   app.config['DEBUG'] = os.getenv('DEBUG', False) -> Option C

4. Quick Check:

   Use getenv with default for safe config [OK]

Hint: Use os.getenv with default to avoid missing keys [OK]

Common Mistakes:

• Using os.environ[] without checking existence
• Not providing default values
• Confusing os.environ.get with os.getenv