Render_template function in Flask - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What does this Flask route render?

Given this Flask route, what will the user see when visiting /hello?

Flask

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

@app.route('/hello')
def hello():
    return render_template('greet.html', name='Alice')

A The content of greet.html with the variable 'name' replaced by 'Alice'.

B A plain text response saying 'Hello Alice'.

C An error because 'name' is not defined in the template.

D A JSON response with {'name': 'Alice'}.

💡 Hint

Think about what render_template does with the variables passed to it.

render_template loads the HTML file and replaces placeholders with the variables given, so the user sees the HTML with 'Alice' where 'name' is used.

📝 Syntax

intermediate

Identify the syntax error in this render_template usage

What is wrong with this Flask route code?

Flask

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

@app.route('/user')
def user():
    return render_template('user.html', username=)

A render_template cannot be used inside a route function.

B Missing value for 'username' keyword argument in render_template.

C The template file 'user.html' must be a Python file.

D Flask app must be run with debug=True to use render_template.

💡 Hint

Check how variables are passed to render_template.

render_template expects keyword arguments like 'username=value'. Here, 'username' is passed without a value, causing a syntax error.

❓ state_output

advanced

What is the output of this Flask route with conditional rendering?

Consider this route and template. What will the user see when visiting /status?

Flask

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

@app.route('/status')
def status():
    user_logged_in = False
    return render_template('status.html', logged_in=user_logged_in)

# status.html content:
# {% if logged_in %}
# <p>Welcome back!</p>
# {% else %}
# <p>Please log in.</p>
# {% endif %}

A <p>Please log in.</p>

B An empty page with no content.

C An error because 'logged_in' is not a boolean.

D <p>Welcome back!</p>

💡 Hint

Look at the value of 'user_logged_in' and the template's if condition.

The variable 'logged_in' is False, so the else block runs, showing 'Please log in.'

🔧 Debug

advanced

Why does this Flask app raise a TemplateNotFound error?

This Flask route raises a TemplateNotFound error. What is the most likely cause?

Flask

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

@app.route('/page')
def page():
    return render_template('mypage.html')

A The route function must return a string, not render_template.

B Flask app must be run with debug=True to find templates.

C The template file 'mypage.html' is missing from the 'templates' folder.

D render_template requires the template file to be in the static folder.

💡 Hint

Check where Flask looks for template files by default.

Flask looks for templates in the 'templates' folder. If 'mypage.html' is missing there, TemplateNotFound error occurs.

🧠 Conceptual

expert

How does Flask's render_template handle variable scope?

When you pass variables to render_template, how are they accessed inside the template?

A Variables are only accessible inside Python code blocks, not in HTML parts.

B Variables must be declared global in the template to be accessed.

C Variables passed are converted to JSON strings and must be parsed in the template.

D Variables passed as keyword arguments become available as template variables with the same names.

💡 Hint

Think about how templates use placeholders for variables.

Flask injects the passed variables into the template context, so you can use them directly by name in the template.

Practice

1. What is the main purpose of the render_template function in Flask?

easy

A. To connect Python code with HTML pages and send data to them

B. To start the Flask web server

C. To handle database connections

D. To create new HTML files automatically

Solution

1. Step 1: Understand what render_template does

   The render_template function is used to link Python code with HTML templates so that dynamic content can be shown on web pages.

2. Step 2: Compare options with this purpose

   Only To connect Python code with HTML pages and send data to them correctly describes this purpose. Options A, B, and C describe unrelated tasks.

3. Final Answer:

   To connect Python code with HTML pages and send data to them -> Option A

4. Quick Check:

   render_template connects Python and HTML [OK]

Hint: Remember: render_template links Python to HTML pages [OK]

Common Mistakes:

• Thinking render_template starts the server
• Confusing render_template with database functions
• Assuming it creates HTML files automatically

2. Which of the following is the correct way to use render_template to show the file home.html?

easy

A. render_template('home.html')

B. render_template(home.html)

C. return render_template(home.html)

D. return render_template('home.html')

Solution

1. Step 1: Check the syntax for render_template

   The function requires the template filename as a string inside quotes and must be returned from the route function.

2. Step 2: Identify the correct option

   return render_template('home.html') correctly uses quotes around the filename and returns the result. Options A and D miss the return statement, and return render_template(home.html) misses quotes around the filename.

3. Final Answer:

   return render_template('home.html') -> Option D

4. Quick Check:

   Use quotes and return the render_template call [OK]

Hint: Always return render_template with filename as a string [OK]

Common Mistakes:

• Forgetting to return the render_template call
• Not putting the filename in quotes
• Calling render_template without return

3. Given this Flask route code:

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

@app.route('/')
def home():
    user = 'Alice'
    return render_template('welcome.html', username=user)

What will the template receive as the variable username?

medium

A. 'Alice'

B. 'user'

C. null

D. An error occurs

Solution

1. Step 1: Understand variable passing in render_template

   The function passes variables as keyword arguments. Here, username=user sends the value of user which is 'Alice'.

2. Step 2: Identify the value received in the template

   The template variable username will have the string 'Alice'. 'Alice' matches this. 'user' is the variable name as string, which is incorrect. null and D are wrong because no error occurs and the value is not null.

3. Final Answer:

   'Alice' -> Option A

4. Quick Check:

   Variable value passed, not variable name [OK]

Hint: render_template passes variable values, not names [OK]

Common Mistakes:

• Passing variable name as string instead of value
• Assuming template gets null if variable not defined
• Expecting an error without syntax issues

4. What is wrong with this Flask route code?

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

@app.route('/')
def index():
    return render_template('index.html', title=Welcome)

medium

A. The template filename should be in double quotes

B. Missing return statement before render_template

C. The variable value Welcome is not in quotes, causing a syntax error

D. render_template cannot accept variables

Solution

1. Step 1: Check the variable argument syntax

   The value passed to title is Welcome without quotes, which Python treats as a name, causing a syntax error.

2. Step 2: Identify the correct fix

   Putting quotes around Welcome (like 'Welcome' or "Welcome") fixes the error. Options A, B, and D are incorrect because quotes can be single or double, return is present, and render_template accepts variables.

3. Final Answer:

   The variable value Welcome is not in quotes, causing a syntax error -> Option C

4. Quick Check:

   String values must be quoted in render_template [OK]

Hint: Put quotes around string values passed to render_template [OK]

Common Mistakes:

• Forgetting quotes around string values
• Thinking return is missing
• Believing render_template can't take variables

5. You want to show a list of products on a webpage using Flask. Which code correctly passes the list products = ['apple', 'banana', 'cherry'] to the template products.html so it can display them?

hard

A. return render_template('products.html', products='products')

B. return render_template('products.html', products=products)

C. return render_template('products.html', items=products)

D. render_template('products.html', products=products)"

Solution

1. Step 1: Understand variable passing to templates

   The variable name used in the template should match the keyword argument name in render_template. Passing the actual list variable as the value is required.

2. Step 2: Identify correct usage

   return render_template('products.html', products=products) passes the list products correctly with the same name. return render_template('products.html', items=products) uses a different name items, which is valid but may confuse if template expects products. return render_template('products.html', products='products') passes a string 'products' instead of the list. render_template('products.html', products=products)" misses the return statement.

3. Final Answer:

   return render_template('products.html', products=products) -> Option B

4. Quick Check:

   Pass list variable with matching name and return it [OK]

Hint: Return render_template with variable name matching template use [OK]

Common Mistakes:

• Passing variable name as string instead of list
• Not returning the render_template call
• Using different variable names without updating template