Parameter type converters (int, float, path) in Flask - Step-by-Step Execution

Concept Flow - Parameter type converters (int, float, path)

Define route with converter

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Request URL received

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Extract parameter from URL

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Apply type converter

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Pass converted value to view function

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Return response with typed parameter

The web server reads the URL, extracts parameters, converts them to the specified type (int, float, or path), then passes them to the function.

Execution Sample

Flask

from flask import Flask
app = Flask(__name__)

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

Defines a route that accepts an integer parameter from the URL and returns it in the response.

Execution Table

Step	URL Part	Converter Applied	Converted Value	Function Parameter	Response
1	/item/42	int	42	id=42	"Item ID is 42"
2	/item/3.14	int	Error	No call	404 Not Found (conversion fails)
3	/item/abc	int	Error	No call	404 Not Found (conversion fails)
4	/price/3.14	float	3.14	price=3.14	"Price is 3.14"
5	/price/42	float	42.0	price=42.0	"Price is 42.0"
6	/files/docs/readme.txt	path	docs/readme.txt	filepath='docs/readme.txt'	"File path is docs/readme.txt"

💡 Execution stops when URL matches route and parameter converts successfully; otherwise 404 error.

Variable Tracker

Variable	Start	After Step 1	After Step 4	After Step 6
id	None	42	None	None
price	None	None	3.14	None
filepath	None	None	None	docs/readme.txt

Key Moments - 2 Insights

Why does accessing /item/3.14 cause a 404 error when using <int:id>?

Because the int converter only accepts whole numbers. The execution_table row 2 shows conversion fails for '3.14', so the function is not called.

What is the difference between <path:filepath> and a normal string parameter?

The path converter accepts slashes inside the parameter, allowing multi-level paths. Normal string stops at the first slash. See execution_table row 6 for example.

Visual Quiz - 3 Questions

Look at the execution_table, what is the function parameter 'price' at step 5?

A 3.14

B 42.0

C 42

D Error

💡 Hint

Check the 'Converted Value' and 'Function Parameter' columns at step 5 in execution_table.

At which step does the path converter handle a parameter with slashes?

A Step 1

B Step 4

C Step 6

D Step 2

💡 Hint

Look for the 'path' converter in the 'Converter Applied' column in execution_table.

If you change <int:id> to <float:id> in the route, what happens at step 2 (/item/3.14)?

A id becomes 3.14 as float

B id becomes 3 as int

C Conversion fails, 404 error

D Function not called

💡 Hint

Refer to how float converter works in execution_table steps 4 and 5.

Concept Snapshot

Flask URL converters:
- <int:name>: accepts integers only
- <float:name>: accepts floating numbers
- <path:name>: accepts strings including slashes
Use converters in route to auto-convert URL parts to Python types.
If conversion fails, Flask returns 404 error.
Pass converted values as function parameters.

Full Transcript

In Flask, you can specify parameter type converters in your route URLs to automatically convert parts of the URL to Python types. Common converters are int for integers, float for decimal numbers, and path for strings that can include slashes. When a request URL matches a route, Flask extracts the parameter and tries to convert it using the specified converter. If conversion succeeds, the converted value is passed to the view function as an argument. If conversion fails, Flask returns a 404 error. For example, a route '/item/<int:id>' only accepts integer IDs. If you visit '/item/42', the id parameter is 42 as an integer. But '/item/3.14' fails because 3.14 is not an integer. The path converter allows slashes inside the parameter, useful for file paths like '/files/docs/readme.txt'. This way, Flask helps you get typed parameters easily from URLs.