Why template engines matter in Flask - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to render a template in Flask.

Flask

from flask import Flask, render_template
app = Flask(__name__)

@app.route('/')
def home():
    return [1]('index.html')

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

Arender_html

Brender_page

Crender_template

Drender_view

Attempts:

3 left

💡 Hint

Common Mistakes

Using a non-existent function like render_html.

Trying to return the template file name as a string.

The render_template function is used in Flask to load and render HTML templates.

2fill in blank

medium

Complete the code to pass a variable to the template.

Flask

from flask import Flask, render_template
app = Flask(__name__)

@app.route('/user/<name>')
def user(name):
    return render_template('user.html', [1]=name)

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

Aname

Busername

Cuser_name

Duser

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different variable name that doesn't match the template.

Forgetting to pass the variable at all.

The variable name used in the template must match the keyword argument passed in render_template. Here, name is passed.

3fill in blank

hard

Fix the error in the template syntax to display a variable.

Flask

<h1>Hello, [1]!</h1>

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

A[[ name ]]

B{% name %}

C{# name #}

D{{ name }}

Attempts:

3 left

💡 Hint

Common Mistakes

Using {% %} which is for logic, not variables.

Using incorrect brackets like [[ ]].

In Flask templates (Jinja2), variables are displayed using double curly braces like {{ name }}.

4fill in blank

hard

Fill both blanks to create a dictionary in a template that filters items with quantity greater than 5.

Flask

{% set filtered = {item: qty for item, qty in inventory.items() if qty [1] 5} %}
<ul>
  {% for item, qty in filtered.items() %}
    <li>[2]: {{qty}}</li>
  {% endfor %}
</ul>

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

A>

Bitem

Cquantity

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' instead of '>' in the filter.

Using 'quantity' which is not the key variable name.

The filter uses '>' to select quantities greater than 5. The dictionary key 'item' is used to display the item name.

5fill in blank

hard

Fill all three blanks to loop over a list of users and display their names in uppercase.

Flask

{% for [1] in [2] %}
  <p>{{ [3].upper() }}</p>
{% endfor %}

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

Auser

Busers

Dusername

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'username' which is not defined.

Mixing variable names between loop and list.

The loop variable is 'user', the list is 'users', and to display the name in uppercase, use 'user.upper()'.

Practice

1. Why do Flask developers use template engines like Jinja2?

easy

A. To separate the website design from the Python code

B. To write all HTML directly inside Python functions

C. To avoid using any HTML in the project

D. To make the website load faster by skipping HTML

Solution

1. Step 1: Understand the role of template engines

   Template engines help keep the design (HTML) separate from the Python logic, making code cleaner.

2. Step 2: Identify the correct purpose in Flask

   Flask uses template engines to insert data into HTML without mixing code and design.

3. Final Answer:

   To separate the website design from the Python code -> Option A

4. Quick Check:

   Separation of concerns = To separate the website design from the Python code [OK]

Hint: Template engines separate code and design for clarity [OK]

Common Mistakes:

• Thinking template engines remove HTML entirely
• Believing all HTML must be inside Python code
• Assuming template engines speed up loading by skipping HTML

2. Which of the following is the correct way to insert a variable name in a Flask template using Jinja2?

easy

A. {{ name }}

B. <% name %>

C. [[ name ]]

D. {% name %}

Solution

1. Step 1: Recall Jinja2 syntax for variables

   Jinja2 uses double curly braces {{ }} to insert variables into templates.

2. Step 2: Match the syntax to the options

   Only {{ name }} uses the correct {{ name }} syntax for variable insertion.

3. Final Answer:

   {{ name }} -> Option A

4. Quick Check:

   Variable insertion = {{ }} [OK]

Hint: Use double curly braces {{ }} for variables in templates [OK]

Common Mistakes:

• Using {% %} which is for control flow, not variables
• Confusing with other template syntaxes like <% %>
• Using brackets or other symbols instead of {{ }}

3. Given this Flask template snippet:

{% if user %}
  Hello, {{ user }}!
{% else %}
  Hello, Guest!
{% endif %}

What will be displayed if user is set to "Alice"?

medium

A. Hello, Guest!

B. Hello, {{ user }}!

C. Hello, Alice!

D. SyntaxError

Solution

1. Step 1: Understand the if-else logic in the template

   The template checks if user has a value. If yes, it shows "Hello, {{ user }}!" with the variable replaced.

2. Step 2: Substitute the variable value

   Since user is "Alice", the output becomes "Hello, Alice!".

3. Final Answer:

   Hello, Alice! -> Option C

4. Quick Check:

   Variable present = personalized greeting [OK]

Hint: If variable exists, template shows its value inside {{ }} [OK]

Common Mistakes:

• Thinking the variable name {{ user }} will print literally
• Ignoring the if condition and choosing the else output
• Assuming a syntax error due to template tags

4. What is wrong with this Flask template code?

{% for item in items %}
  
{{ item }
{% endfor %}

medium

A. Incorrect for loop syntax in Jinja2

B. Missing closing curly brace in variable tag

C. The <p> tag cannot be used inside loops

D. No need to use {% endfor %} in templates

Solution

1. Step 1: Check the variable tag syntax

   The variable tag {{ item } is missing one closing curly brace '}' at the end.

2. Step 2: Verify loop and HTML tags

   The for loop syntax and <p> tags are correct; only the variable tag is wrong.

3. Final Answer:

   Missing closing curly brace in variable tag -> Option B

4. Quick Check:

   Variable tags need double braces {{ }} [OK]

Hint: Count your curly braces carefully in {{ }} tags [OK]

Common Mistakes:

• Forgetting the second closing brace in {{ }}
• Thinking {% endfor %} is optional
• Believing HTML tags can't be inside loops

5. You want to display a list of products with their prices in a Flask template. Which approach best uses a template engine to keep your code clean and easy to update?

hard

A. Write all HTML and Python code together in the Flask route function

B. Generate the entire HTML page as a single string in Python and return it

C. Hardcode the product list in the HTML template without variables

D. Use a template with a for loop to list products and insert prices dynamically

Solution

1. Step 1: Understand separation of concerns

   Keeping HTML in templates and logic in Python functions makes code organized and maintainable.

2. Step 2: Use template loops for dynamic lists

   Using a for loop in the template to display products with prices allows easy updates and clean code.

3. Final Answer:

   Use a template with a for loop to list products and insert prices dynamically -> Option D

4. Quick Check:

   Templates + loops = clean dynamic pages [OK]

Hint: Use template loops to display lists dynamically [OK]

Common Mistakes:

• Mixing HTML and Python code in one place
• Hardcoding data instead of using variables
• Building HTML strings manually in Python