url_for() is broken with multiple same blueprint

[sergiokessler]

my situation is something like this:

api.py

def blueprint_maker(bpname, db_session):

    api = Blueprint(bpname, __name__)
    [...]
    @api.route('/ping', methods=['GET'])
    def ping():
        response = {
            'data': [{
                'echo': 'echo!',
                'source': url_for('api.ping')
            }]
        }
        return jsonify(response)

    return api

and then:

main.py

[snip]
ar = blueprint_maker('ar', SessionLocal_ar)
uy = blueprint_maker('uy', SessionLocal_uy)
br = blueprint_maker('uy', SessionLocal_br)
pt = blueprint_maker('uy', SessionLocal_pt)
[...]


app.register_blueprint(ar, url_prefix='/ar')
app.register_blueprint(uy, url_prefix='/uy')
app.register_blueprint(ar, url_prefix='/br')
app.register_blueprint(uy, url_prefix='/pt')
[...]

I expected url_for() to just work in this scenario, but instead, it gives me:

Could not build url for endpoint 'api.ping'. Did you mean 'ar.ping' instead?

isn't this supposed to work?

Environment:

• Python version: 3.9
• Flask version: 2

[davidism]

As the error says, you need to specify the URL you want to build. The url takes the form bp_name.view_name. The bp name is ar, uy, etc.

[sergiokessler]

Maybe I was not clear, but there is ONE api.py, and at that point I don't know how the name will be later...

I tried

url_for(f'{bpname}.ping')

but that didn't work (it just gives me the relative url, not the full one)

[tachyondecay]

Call url_for() with _external=True to generate an absolute URL.

Also note you can pass a name argument to register_blueprint to register the same blueprint with multiple unique names (more info).

[sergiokessler]

thanks!

this is the code to make it work:
(note that I can't hardcode the blueprint name here)

def blueprint_maker(bpname, db_session):

    api = Blueprint(bpname, __name__)
    [... do stuff with db_session ...]
    @api.route('/ping', methods=['GET'])
    def ping():
        response = {
            'data': [{
                'echo': 'echo!',
                'source': url_for(f'{bpname}.ping', _external=True)
            }]
        }
        return jsonify(response)

    return api

(and yes, I'm using the name argument to register the same bp multiple times, but the bp implementation does not know what will be those names)