Serving CSS files in Flask - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to serve static CSS files in Flask.

Flask

app = Flask(__name__, static_folder=[1])

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

A"static"

B"templates"

C"assets"

D"css"

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'templates' folder for static files

Using incorrect folder names like 'css' or 'assets'

Flask serves static files from the folder named "static" by default. Setting static_folder="static" tells Flask where to find CSS files.

2fill in blank

medium

Complete the HTML code to link a CSS file named 'style.css' located in the static folder.

Flask

<link rel="stylesheet" href="{{ url_for([1], filename='style.css') }}">

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

A"styles"

B"static"

C"css"

D"static_files"

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect endpoint names like 'css' or 'styles'

Forgetting to use url_for function

In Flask, url_for('static', filename='style.css') generates the correct URL to the CSS file inside the static folder.

3fill in blank

hard

Fix the error in the Flask route to serve a CSS file manually.

Flask

@app.route('/css/<path:filename>')
def send_css(filename):
    return send_from_directory([1], filename)

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

A"assets/css"

B"templates/css"

C"css"

D"static/css"

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'templates/css' which is for HTML templates

Using just 'css' without 'static' prefix

To serve CSS files manually, the directory path should point to the CSS folder inside the static folder, which is 'static/css'.

4fill in blank

hard

Fill both blanks to create a dictionary comprehension that maps CSS filenames to their sizes in bytes from the static/css folder.

Flask

css_files = {filename: os.path.getsize(os.path.join([1], filename)) for filename in os.listdir([2]) if filename.endswith('.css')}

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

A"static/css"

B"static"

C"templates/css"

D"assets/css"

Attempts:

3 left

💡 Hint

Common Mistakes

Using different folder paths for listing and size

Using 'templates/css' which is incorrect

Both blanks should be 'static/css' to correctly access the CSS files folder for listing and size checking.

5fill in blank

hard

Fill all three blanks to create a Flask route that serves a CSS file from the static folder with caching headers.

Flask

@app.route('/styles/<path:filename>')
def styles(filename):
    response = send_from_directory([1], filename)
    response.headers['Cache-Control'] = [2]
    response.headers['Content-Type'] = [3]
    return response

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

A"static/css"

B"public/css"

C"no-cache, max-age=3600"

D"text/css"

Attempts:

3 left

💡 Hint

Common Mistakes

Wrong folder path

Wrong Cache-Control value

Wrong Content-Type header

The CSS files are served from 'static/css'. The Cache-Control header sets caching rules, and Content-Type must be 'text/css' for CSS files.

Practice

1. Where should you place CSS files in a Flask project to serve them correctly?

easy

A. Inside the css folder anywhere

B. Inside the static folder

C. In the root project directory

D. Inside the templates folder

Solution

1. Step 1: Understand Flask static file serving

   Flask automatically serves files placed inside the static folder.

2. Step 2: Identify correct folder for CSS

   CSS files must be inside the static folder to be served properly.

3. Final Answer:

   Inside the static folder -> Option B

4. Quick Check:

   CSS files go in static folder [OK]

Hint: Put CSS in the static folder for Flask to serve it [OK]

Common Mistakes:

• Placing CSS in templates folder
• Putting CSS in root directory
• Creating a separate css folder outside static

2. Which is the correct way to link a CSS file named style.css in a Flask HTML template?

easy

A. <link rel="stylesheet" href="{{ url_for('static', filename='style.css') }}">

B. <link rel="stylesheet" href="/style.css">

C. <link rel="stylesheet" href="static/style.css">

D. <link rel="stylesheet" href="{{ url_for('templates', filename='style.css') }}">

Solution

1. Step 1: Use url_for to link static files

   Flask uses url_for('static', filename='...') to generate correct URLs for static files.

2. Step 2: Correct syntax in HTML template

   The link tag must use {{ url_for('static', filename='style.css') }} inside the href attribute.

3. Final Answer:

   <link rel="stylesheet" href="{{ url_for('static', filename='style.css') }}"> -> Option A

4. Quick Check:

   Use url_for('static', filename=...) for CSS links [OK]

Hint: Use url_for('static', filename='file.css') in href [OK]

Common Mistakes:

• Linking CSS without url_for
• Using 'templates' instead of 'static'
• Incorrect href paths

3. Given this Flask template snippet, what will be the rendered HTML for linking main.css if the app runs on http://localhost:5000?

<link rel="stylesheet" href="{{ url_for('static', filename='main.css') }}">

medium

A.

B.

C.

D.

Solution

1. Step 1: Understand url_for output for static files

   By default, url_for('static', filename='main.css') returns the path starting with /static/ without domain.

2. Step 2: Rendered HTML link tag

   The rendered HTML will have href="/static/main.css" which is relative to the server root.

3. Final Answer:

   <link rel="stylesheet" href="/static/main.css"> -> Option A

4. Quick Check:

   url_for('static', filename=...) returns path starting with /static/ [OK]

Hint: url_for('static', ...) returns path starting with /static/ [OK]

Common Mistakes:

• Expecting full URL with domain
• Missing leading slash in href
• Using relative path without /static/

4. You wrote this in your Flask template to link CSS:

<link rel="stylesheet" href="{{ url_for('static', filename='styles.css') }}">

But the CSS is not loading. What is the most likely error?

medium

A. The CSS file name is misspelled in the url_for call

B. You forgot to include rel="stylesheet" in the link tag

C. You used url_for('templates', filename='styles.css') instead

D. The CSS file is not inside the static folder

Solution

1. Step 1: Check file location for static serving

   Flask only serves files placed inside the static folder automatically.

2. Step 2: Confirm file placement

   If the CSS file is outside static, Flask won't find it even if the link is correct.

3. Final Answer:

   The CSS file is not inside the static folder -> Option D

4. Quick Check:

   CSS must be inside static folder to load [OK]

Hint: Check CSS file is inside static folder if not loading [OK]

Common Mistakes:

• Placing CSS outside static folder
• Misspelling filename in url_for
• Using wrong folder name in url_for

5. You want to serve multiple CSS files in Flask: reset.css and theme.css. Both are inside the static/css folder. How should you link them correctly in your HTML template?

hard

A. <link rel="stylesheet" href="/static/reset.css">
<link rel="stylesheet" href="/static/theme.css">

B. <link rel="stylesheet" href="{{ url_for('static', filename='reset.css') }}">
<link rel="stylesheet" href="{{ url_for('static', filename='theme.css') }}">

C. <link rel="stylesheet" href="{{ url_for('static', filename='css/reset.css') }}">
<link rel="stylesheet" href="{{ url_for('static', filename='css/theme.css') }}">

D. <link rel="stylesheet" href="static/css/reset.css">
<link rel="stylesheet" href="static/css/theme.css">

Solution

1. Step 1: Understand folder structure for static files

   Files inside static/css must be referenced with css/filename in url_for.

2. Step 2: Use url_for with correct filename path

   Link tags must use {{ url_for('static', filename='css/reset.css') }} and similarly for theme.css.

3. Final Answer:

   Use url_for with 'css/reset.css' and 'css/theme.css' -> Option C

4. Quick Check:

   Include subfolder in filename for nested static files [OK]

Hint: Include subfolder path in filename for nested static files [OK]

Common Mistakes:

• Omitting 'css/' folder in filename
• Hardcoding paths without url_for
• Using wrong folder names in href