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Flask Academy · Lesson

Type Converters: int, float, string, path

Constrain URL segments with built-in converters.

Type Converters: int, float, string, path is a free Flask Academy lesson on CoddyKit — lesson 2 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Flask Academy learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.

Strings Are Not Always Enough

Captured values default to strings, but /post/42 should give a number, not text. A converter tells Flask what type to expect in that segment.

Converter Syntax

Put the converter name before the variable with a colon. The pattern is <converter:name>, and Flask applies it before calling your view.

@app.route('/post/<int:post_id>')
def show(post_id):
    return str(post_id + 1)

The int Converter

Use int to capture whole numbers. /post/42 hands your view the integer 42, so you can do math without calling int() yourself. 🔢

@app.route('/page/<int:n>')
def page(n):
    return f'Page {n}'

int Rejects Non-Numbers

A converter also filters URLs. /page/abc will not match an int route, so Flask returns 404 instead of crashing inside your function.

The float Converter

Use float for decimal numbers like prices or ratings. /rate/4.5 gives you the float 4.5, ready for arithmetic right away.

@app.route('/rate/<float:score>')
def rate(score):
    return str(score * 2)

The string Converter

string is the default: it accepts any text but stops at a slash. You rarely write it explicitly since plain <name> already behaves this way.

@app.route('/tag/<string:label>')
def tag(label):
    return label

The path Converter

Use path when the value can contain slashes, like a folder route. Unlike string, it captures /docs/intro/setup as one whole value.

@app.route('/files/<path:filepath>')
def serve(filepath):
    return filepath

Pick the Right Tool

Match the converter to your data: int for ids, float for decimals, string for words, path for slashed routes. The right choice prevents bad input early.

Converters Validate for You

By rejecting mismatched URLs with a 404, converters act as a first line of validation. Your view only runs when the type already fits.

Combine in One Route

You can mix converters across segments. Here an int id and a string tab live in the same path, each typed independently.

@app.route('/user/<int:uid>/<tab>')
def view(uid, tab):
    return f'{uid}:{tab}'

Negatives and Edge Cases

The built-in int converter matches only non-negative whole numbers by default. For minus signs or stricter rules, you would write a custom converter later.

Quick Check

Which converter lets a captured value include slashes, like docs/intro/setup?

Recap: You Typed Your URLs

Converters give captured values a type and reject bad input with a 404. Remember int, float, string, and path. Next: building URLs safely. 🧭

Frequently asked questions

Is the “Type Converters: int, float, string, path” lesson free?

Yes — the full text of “Type Converters: int, float, string, path” is free to read here on the web, and the Flask Academy course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Flask Academy course, upgrade to CoddyKit PRO.

What will I learn in “Type Converters: int, float, string, path”?

Constrain URL segments with built-in converters. You practise Flask Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start Flask Academy?

No prior experience is required. Flask Academy on CoddyKit is structured for beginners through advanced learners; this is — lesson 2 of 4, so you can start here or from the beginning and move at your own pace.

How long does the “Type Converters: int, float, string, path” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this Flask Academy lesson?

Yes. Every Flask Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

All lessons in this course

  1. Capture Variables from the Path
  2. Type Converters: int, float, string, path
  3. Build URLs with url_for
  4. Trailing Slashes and Redirect Behavior
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