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.