Variable substitution syntax in Flask - Practice Problems & Coding Challenges

Challenge - 5 Problems

📝 Syntax

intermediate

What is the output of this Flask template code?

Given the Flask template snippet below, what will be rendered when name = 'Alice' is passed to the template?

Flask

Hello, {{ name }}!

A Hello, name!

B Hello, {{ name }}!

C Hello, !

D Hello, Alice!

💡 Hint

Remember that double curly braces {{ }} are used to insert variable values in Flask templates.

In Flask templates, {{ name }} is replaced by the value of the variable 'name'. So if name is 'Alice', the output is 'Hello, Alice!'.

❓ component_behavior

intermediate

What happens if a variable is missing in Flask template substitution?

Consider this Flask template code:
User: {{ username }}
If the variable username is not provided in the template context, what will be rendered?

A User: {{ username }}

B User:

C User: None

D Template rendering error

💡 Hint

Flask's template engine replaces missing variables with empty strings by default.

If a variable is missing, Flask's Jinja2 template engine inserts an empty string instead of raising an error or showing the variable name.

🔧 Debug

advanced

Identify the error in this Flask template variable substitution

What error will occur when rendering this Flask template?
Hello, {{ user.name }!

A SyntaxError due to missing closing brace

B NameError because 'user' is undefined

C No error, renders 'Hello, '

D TypeError because 'user' is not an object

💡 Hint

Check the syntax of the variable substitution braces carefully.

The template has a missing closing curly brace '}}' after 'user.name'. This causes a syntax error during template rendering.

❓ state_output

advanced

What is the output of this Flask template with filters?

Given the Flask template:
{{ message|upper }}
and the context {'message': 'hello world'}, what is the rendered output?

A HELLO WORLD

B {{ message|upper }}

C hello world

D Hello World

💡 Hint

The filter 'upper' converts text to uppercase.

The 'upper' filter changes all letters to uppercase, so 'hello world' becomes 'HELLO WORLD'.

🧠 Conceptual

expert

Which option correctly escapes HTML in Flask variable substitution?

In Flask templates, how does variable substitution handle HTML special characters by default?
Given text = 'bold', what will {{ text }} render as?

A SyntaxError

B <b>bold</b>

C &lt;b&gt;bold&lt;/b&gt;

D &amp;lt;b&amp;gt;bold&amp;lt;/b&amp;gt;

💡 Hint

Flask templates escape HTML characters to prevent code injection by default.

Flask's Jinja2 escapes HTML special characters like < and > to their safe equivalents < and > to avoid rendering raw HTML.