Explain default `_method` used for `url_for()` #5536

xArbisRox · 2024-07-29T09:42:08Z

xArbisRox
Jul 29, 2024

Hello folks,
I stumbled upon an unexpected behavior recently, which I assume might be worth to pick up in the documentation.

Let's take this simple application:

app.py

from flask import Flask, redirect, url_for, render_template

app = Flask(__name__)


@app.route('/')
def index():
    return render_template("index.html")


@app.route("/target", methods=["POST"])
@app.route("/target/<arg>", methods=["GET"])
def target(arg=None):
    return arg


@app.route("/redirecter/<arg>", methods=["GET", "POST"])
def redirecter(arg):
    return redirect(url_for('target', arg=arg))


if __name__ == '__main__':
    app.run()

index.html

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Flask</title>
</head>
<body>
<form method="POST"
      action="{{ url_for('redirecter', arg='POSTFromForm') }}">
    <input type="submit" value="POST">
</form>
<form method="GET"
      action="{{ url_for('redirecter', arg='GETFromForm') }}">
    <input type="submit" value="GET">
</form>
</body>
</html>

I would see this as a typical scenario, having a route without path arguments for POST requests and another endpoint with path arguments for GET requests in the target route.

However, when I send a POST request to the redirecter, url_for("target", arg=arg) generates '/target?arg=xyz'. When I send a GET request to the redirecter, it will generate the expected '/target/xyz'.

I can fix the redirecter for the POST request by explicitely defining url_for("target", arg=arg, _method="GET").
So I could adjust the redirecter to something like:

@app.route("/redirecter/<arg>", methods=["GET", "POST"])
def redirecter(arg):
    if request.method == "POST":
        return redirect(url_for("target", arg=arg, _method="GET"))
    return redirect(url_for('target', arg=arg))

I do understand, why this is happening. For the POST method, there is no endpoint including <arg> defined, which is why url_for() cannot resolve it and appends it as query argument thereafter.

However, this is the point where I am going to. For me, it was not intuitive, that url_for() uses the method of the current request context to generate its output. Currently, the documentation states:

_method (str | None) – If given, generate the URL associated with this method for the endpoint.

Might this be worth to pick up in the documentation?

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Explain default `_method` used for `url_for()` #5536

{{title}}

Replies: 0 comments

Select a reply

Explain default _method used for url_for() #5536

xArbisRox Jul 29, 2024

Replies: 0 comments

Explain default `_method` used for `url_for()` #5536

xArbisRox
Jul 29, 2024