Parameter type converters (int, float, path) in Flask - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output when accessing a route with converter?

Consider this Flask route:

from flask import Flask
app = Flask(__name__)

@app.route('/item/<int:id>')
def item(id):
    return f"Item ID is {id}"

What will be the response when visiting /item/42 in the browser?

Flask

from flask import Flask
app = Flask(__name__)

@app.route('/item/<int:id>')
def item(id):
    return f"Item ID is {id}"

A Item ID is 42

B Item ID is '42'

C 404 Not Found error

D TypeError because id is not an int

💡 Hint

The converter ensures the parameter is an integer.

The converter converts the URL part to an integer before passing it to the function. So id is the integer 42, and the returned string is 'Item ID is 42'.

📝 Syntax

intermediate

Which route definition correctly uses the converter?

You want to create a Flask route that accepts a floating-point number as a URL parameter named price. Which of these route decorators is correct?

A @app.route('/cost/<price:float>')

B @app.route('/cost/<price>')

C @app.route('/cost/<float_price>')

D @app.route('/cost/<float:price>')

💡 Hint

The converter syntax is <converter:name>.

The correct syntax is . Option D reverses the order, C uses an invalid name, and D has no converter so price is a string.

🔧 Debug

advanced

Why does this route cause a 404 error for a path with slashes?

Given this Flask route:

@app.route('/files/<path:filename>')
def files(filename):
    return f"File requested: {filename}"

What happens when you visit /files/docs/manual.pdf? Why might a similar route without path: cause a 404 error?

Flask

@app.route('/files/<path:filename>')
def files(filename):
    return f"File requested: {filename}"

A The route matches but filename is only 'manual.pdf'; 'path:' has no effect.

B The route causes a 404 because 'path:' is invalid syntax in Flask routes.

C The route matches and filename is 'docs/manual.pdf'; without 'path:' it would only match 'docs' causing 404.

D The route matches but filename is a list of path parts, not a string.

💡 Hint

The 'path' converter allows slashes in the parameter.

The 'path' converter captures the entire remaining path including slashes. Without it, Flask treats the parameter as a string stopping at the first slash, so '/files/docs/manual.pdf' won't match and returns 404.

❓ state_output

advanced

What is the type and value of the parameter inside the view function?

Examine this Flask route:

@app.route('/price/<float:cost>')
def show_price(cost):
    return f"Cost is {cost} and type is {type(cost).__name__}"

What will be the output when visiting /price/19.99?

Flask

@app.route('/price/<float:cost>')
def show_price(cost):
    return f"Cost is {cost} and type is {type(cost).__name__}"

A Cost is '19.99' and type is str

B Cost is 19.99 and type is float

C Cost is 19 and type is int

D Cost is 19.99 and type is str

💡 Hint

The converter converts the parameter to a float type.

The converter converts the URL part to a float before passing it to the function. So cost is the float 19.99, and the type is float.

🧠 Conceptual

expert

Why use converter instead of for file paths?

In Flask routing, what is the main reason to use the <path:filename> converter instead of the default <string:filename> when accepting file paths as parameters?

A <path:> allows slashes in the parameter, so it can capture nested paths; <string:> stops at the first slash.

B <path:> automatically decodes URL-encoded characters; <string:> does not.

C <path:> converts the parameter to a list of strings; <string:> keeps it as a single string.

D <path:> is faster to process than <string:> for long strings.

💡 Hint

Think about how URLs with slashes are matched by Flask converters.

The converter captures the entire remaining path including slashes, allowing nested paths. The default converter stops at the first slash, so it cannot capture nested paths.

Practice

1. What does the int converter do in a Flask route parameter like <int:id>?

easy

A. It matches any text including slashes.

B. It ensures the parameter is an integer and converts it automatically.

C. It converts the parameter to a string.

D. It converts the parameter to a floating-point number.

Solution

1. Step 1: Understand the role of int converter

   The int converter tells Flask to accept only integer values for that URL part.

2. Step 2: Check what happens with the parameter

   Flask automatically converts the matched URL part to an integer type before passing it to the view function.

3. Final Answer:

   It ensures the parameter is an integer and converts it automatically. -> Option B

4. Quick Check:

   int converter = integer parameter [OK]

Hint: int converter means only whole numbers allowed [OK]

Common Mistakes:

• Thinking int converts to string
• Confusing int with float converter
• Assuming int matches any text

2. Which of the following is the correct syntax to define a Flask route that accepts a floating-point number parameter named price?

easy

A. @app.route('/item/<path:price>')

B. @app.route('/item/<int:price>')

C. @app.route('/item/<float:price>')

D. @app.route('/item/<str:price>')

Solution

1. Step 1: Identify the correct converter for floating-point numbers

   The float converter is used to accept decimal numbers in the URL.

2. Step 2: Match the syntax for route parameter

   The correct syntax is <float:price> inside the route decorator.

3. Final Answer:

   @app.route('/item/<float:price>') -> Option C

4. Quick Check:

   float converter = decimal number parameter [OK]

Hint: Use for decimal numbers in route parameters [OK]

Common Mistakes:

• Using int instead of float for decimals
• Using str which is not a Flask converter
• Using path which allows slashes, not numbers

3. Given this Flask route:

@app.route('/files/<path:filename>')
def show_file(filename):
    return f"File requested: {filename}"

What will be the output if the URL is /files/docs/manual.pdf?

medium

A. File requested: docs/manual.pdf

B. File requested: manual.pdf

C. 404 Not Found error

D. File requested: docs

Solution

1. Step 1: Understand the path converter behavior

   The path converter matches the entire remaining path including slashes.

2. Step 2: Analyze the URL and parameter value

   The URL /files/docs/manual.pdf matches filename as docs/manual.pdf.

3. Final Answer:

   File requested: docs/manual.pdf -> Option A

4. Quick Check:

   path converter = matches full path with slashes [OK]

Hint: path converter captures slashes in URL parts [OK]

Common Mistakes:

• Assuming path stops at first slash
• Expecting 404 error for slashes in parameter
• Confusing path with string converter

4. What is wrong with this Flask route definition?

@app.route('/product/<int:product_id>/<float:price>')
def show_product(product_id, price):
    return f"Product {product_id} costs {price}"

When accessing /product/abc/19.99, what error occurs?

medium

A. ValueError because 'abc' is not an integer

B. TypeError because price is not a float

C. No error, it works fine

D. 404 Not Found error due to URL mismatch

Solution

1. Step 1: Check the int converter requirement

   The first parameter expects an integer, but 'abc' is not an integer.

2. Step 2: Understand Flask routing behavior on type mismatch

   Flask does not raise ValueError but returns 404 Not Found if the URL does not match the route pattern.

3. Final Answer:

   404 Not Found error due to URL mismatch -> Option D

4. Quick Check:

   Type mismatch in route = 404 error [OK]

Hint: Wrong type in URL parameter causes 404, not exception [OK]

Common Mistakes:

• Expecting Python exceptions instead of 404
• Confusing ValueError with Flask routing errors
• Assuming route matches any string

5. You want to create a Flask route that accepts a file path parameter which may include slashes, and an integer version number after it, like /download/docs/manual/2. Which route definition correctly uses converters to achieve this?

hard

A. @app.route('/download/<path:filepath>/<int:version>')

B. @app.route('/download/<int:version>/<path:filepath>')

C. @app.route('/download/<path:filepath><int:version>')

D. @app.route('/download/<path:filepath>/<float:version>')

Solution

1. Step 1: Identify the order of parameters in the URL

   The URL pattern is /download/ followed by a path (which may include slashes), then a slash, then an integer version.

2. Step 2: Use path for filepath and int for version in correct order

   The route must be /download/<path:filepath>/<int:version> to match the URL structure.

3. Final Answer:

   @app.route('/download/<path:filepath>/<int:version>') -> Option A

4. Quick Check:

   path then int in route matches URL structure [OK]

Hint: Use path converter before int for multi-part paths [OK]

Common Mistakes:

• Swapping parameter order
• Missing slash between parameters
• Using float instead of int for version