url_for can't distinguish a blueprint mounted two times

[iurisilvio]

Based on blueprint concept, I expected it to handle relative url_for nicely:

from flask import Blueprint, Flask, url_for

bp = Blueprint('foo', __name__)

@bp.route('/')
def func():
    return url_for('.func')

app = Flask(__name__)
app.register_blueprint(bp, url_prefix='/foo')
app.register_blueprint(bp, url_prefix='/bar')

client = app.test_client()
print client.get('/foo/').data
print client.get('/bar/').data

Both prints write the URL to the first blueprint registered (/foo/). Is it possible to mount two times the same blueprint and make relative url_for work? Is this behaviour expected?

[jackunion]

@iurisilvio this is expected behaviour. It won't work with absolute name (i.e. blueprint_name.func) either. What are you trying to do exactly? Probably you should use request.url instead of url_for.

[iurisilvio]

@jackunion it was just an example. I want to mount the same blueprint with different prefixes and I expect my relative url_for to work inside my blueprint, but this is not how it works.

I fixed my problem with multiple blueprints (with the same routes), but I expected url_for working fine with blueprints.

Flask store the blueprint in a dict like dict[blueprint.name] = blueprint. I can change the blueprint name before register the blueprint again and it works (or override the app.register_blueprint to avoid name collision). I'm not sure if it really works.

[jackunion]

@iurisilvio actually, url_for works just fine :]
Try print(app.url_map) to see all url rules.

[untitaker]

I am really curious what you're trying to do with registering the same blueprint multiple times. The restriction might seem arbitrary, but i can imagine it is in place to avoid gross misuse of Flask's blueprints.

[danielchatfield]

Register a blueprint multiple times on an application with different URL rules.

[danielchatfield]

From http://flask.pocoo.org/docs/blueprints/

[danielchatfield]

@iurisilvio this is expected behaviour. It won't work with absolute name (i.e. blueprint_name.func) either.

That is not true. This is not expected behaviour, this is a supported use case.

[jackunion]

@danielchatfield have you read the question?

[danielchatfield]

Yes. The docs give registering a single blueprint multiple times on the same app as an "intended use case".

The utility of that is somewhat questionable if url_for doesn't work properly.

[iurisilvio]

@untitaker I have a blueprint mounted in /foo, but I also want almost the same views in routes like /x/foo and /y/foo, where x and y are sections of my app. Some users can view only x section, which contains lots of routes from other blueprints too. Other users can view x, y and the /foo, which contains data from both sections and some other things.

In most cases, I'd prefer /something/x and /something/y, but this is not the case, x and y are used in several parts of my app and really makes sense in this case.

I just created a blueprint factory to fix this issue for me, using different names. It works fine and is not a huge problem for me. But I consider it a bug, because it is an intended use case (@danielchatfield already quoted it). I never expected a relative url_for returning something from other mounted blueprint.

[untitaker]

First, i have to admit that it indeed seems to be an intended usecase.

@iurisilvio It basically seems like you're mixing code and data there. Adding a rule /<section>/foo and using a proper data storage for the sections seems better at first glance, but i don't want to say your solution is wrong since i don't know your usecase.

[iurisilvio]

Yes, I agree. This structure is weird, but it is really the right choice for my app.

As I said, it was easy to workaround this issue, but if I rather mount the same blueprint in different paths. Blueprints are perfect to my use case, based on blueprint definition. Unfortunately, url_for breaks all my url references. Looks like a bug or at least docs deserve better explanation about this limitation.

[jackunion]

@danielchatfield this question is about url_for, not about registering multiple blueprints.

[iurisilvio]

@jackunion this issue is about the url_for behaviour with the same blueprint registered more than once.

Two statements from blueprints docs:

Register a blueprint multiple times on an application with different URL rules.

Additionally if you are in a view function of a blueprint or a rendered template and you want to link to another endpoint of the same blueprint, you can use relative redirects by prefixing the endpoint with a dot only

[jackunion]

@iurisilvio and again:
url_for will not work as you expect even with absolute name (i.e. blueprint_name.view_func), not only with relative name.
It will give you the wrong url even if your blueprint is registered once but have more than one route decorator (i.e @blueprint_name.route()).
If you want to know how exactly url_for builds url, start here.