From hi at jnnkb.eu  Fri Dec  3 07:54:04 2021
From: hi at jnnkb.eu (jnnk)
Date: Fri, 3 Dec 2021 13:54:04 +0100
Subject: [Flask] URL Map Converters
Message-ID: <9E31C121-6329-430D-B49C-40E056F33703@jnnkb.eu>

Hey everybody,

I yesterday tried using an IDSlugConverter similar to this <https://stackoverflow.com/questions/27760307/create-a-url-with-an-articles-title> with a current version of Werkzeug, which worked without any problems until 0.16.0. Unfortuantly any version >= 1.0.0 leads to the following error:

  File "<werkzeug routing>", line 1, in <builder:'/files/<id_slug:id>'>
    
  File "test_urlmap_converter/flask_app.py", line 20, in to_url
    return f"{value.id}/{value.filename}"
AttributeError: 'int' object has no attribute ?id?
I create the following minimal example to illustrate the problem. The error occurs when navigating to /files/3/hey.txt.

from flask import Flask, url_for
from werkzeug.routing import BaseConverter


class File:
    def __init__(self, id_, filename):
        self.id = id_
        self.filename = filename


class IDSlugConverter(BaseConverter):
    """Matches an int id and optional slug, separated by "/"."""

    regex = r"-?\d+(?:/[\w\-]*.\w*)?"

    def to_python(self, value):
        return int((value.split("/"))[0])

    def to_url(self, value):
        return f"{value.id}/{value.filename}"


app = Flask(__name__)
app.url_map.converters["id_slug"] = IDSlugConverter


@app.route("/")
def index():
    url = url_for("serve_file", id=File(3, "hey.txt"))
    return f'<a href="{url}">Bild</a>'


@app.route("/files/<id_slug:id>")
def serve_file(id):
    return "fancy file"
It seems like these converters now require that to_python and to_url are inverses. Is this intended? Since I?m using this with different model classes I otherwise would have to use some magic like below to prevent circular imports. (See attached app.zip)

def __init__(self, url_map, model):
    module, variable = model.rsplit(".", 1)
    self.model = getattr(sys.modules[module], variable)
    super().__init__(url_map)
With kind regards,

jnnk


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From skip.montanaro at gmail.com  Mon Dec 27 06:32:45 2021
From: skip.montanaro at gmail.com (Skip Montanaro)
Date: Mon, 27 Dec 2021 05:32:45 -0600
Subject: [Flask] Confused by an unexpected route-to-function mapping
Message-ID: <CANc-5UyT11mUDj45trbWhBzZPMa4kpBWt=SMrd0tUCxGkMoYuw@mail.gmail.com>

I'm returning to Flask after several years away (and never having done much
of any significance with it before). I'm having trouble with the mapping
between routes and the functions which handle them.

I have two functions, each of which is meant to handle a number of related
routes. The first is just supposed to normalize things and do a permanent
redirect to the second

@app.route('/<int:year>-<int:month>/html/<filename>')
@app.route('/CR/<int:year>-<int:month>/html/<filename>')
@app.route('/<int:year>-<int:month>')
@app.route('/<int:year>-<int:month>/<filename>')
def old_cr_month(year, month, filename="index.html"):
    print(">> old_cr_month:", year, month, filename)

    raise Exception

    return redirect(url_for("cr", year=year, month=month,
                            filename=filename),
                    code=301)


@app.route("/CR")
@app.route("/CR/")
@app.route('/CR/<int:year>/<int:month>')
@app.route('/CR/<int:year>/<int:month>/<filename>')
def cr(year=None, month=None, filename="index.html"):
    print(">> cr:", year, month, filename)
    ...


When I visit this URL:

http://super.secret.website/CR/2000-09/html/maillist.html


old_cr_month is called, as I expect. Its print function is called and the
embedded exception is raised.

When I visit this URL:

http://super.secret.website/CR/2000-09/html/threads.html


the old_cr_month handler isn't called. Instead, the cr function is enlisted
to handle the request and its print function is called. Strangely, it does
seem to get year, month and filename correct. This despite none of the
defined routes for cr having URL templates with either the year-month form
or an embedded html directory in the middle.

When I dump the app object in the debugger the displayed url_map looks to
me like old_cr_month should have handled the URL (my candidate route
mapping highlighted in red).

Map([<Rule '/hello' (HEAD, OPTIONS, GET) -> hello>,
 <Rule '/CR/' (HEAD, OPTIONS, GET) -> cr>,
 <Rule '/CR' (HEAD, OPTIONS, GET) -> cr>,
 <Rule '/' (HEAD, OPTIONS, GET) -> index>,
 <Rule '/CR/<year>-<month>/html/<filename>' (HEAD, OPTIONS, GET) ->
old_cr_month>,
 <Rule '/<year>-<month>/html/<filename>' (HEAD, OPTIONS, GET) ->
old_cr_month>,
 <Rule '/static/<filename>' (HEAD, OPTIONS, GET) -> static>,
 <Rule '/CR/<year>/<month>/<msg>' (HEAD, OPTIONS, GET) -> cr_message>,
 <Rule '/CR/<year>/<month>/<filename>' (HEAD, OPTIONS, GET) -> cr>,
 <Rule '/CR/<year>/<month>' (HEAD, OPTIONS, GET) -> cr>,
 <Rule '/<year>-<month>/<filename>' (HEAD, OPTIONS, GET) -> old_cr_month>,
 <Rule '/<year>-<month>' (HEAD, OPTIONS, GET) -> old_cr_month>])


Here's my setup:

$ flask --version
Python 3.10.1
Flask 2.0.2
Werkzeug 2.0.2


I'm running in an Ubuntu 20.04 VM.

What am I missing about routes here? How can two so similarly structured
URLs be mapped to different handler functions? Is there something I can do
to dig into the URL-to-handler mapping process?

Thx,

Skip Montanaro
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