327

Is it possible to directly declare a flask URL optional parameter?

Currently I'm proceeding the following way:

@user.route('/<userId>')
@user.route('/<userId>/<username>')
def show(userId, username=None):
    pass

How can I directly say that username is optional?

daaawx
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Noor
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11 Answers11

451

Another way is to write

@user.route('/<user_id>', defaults={'username': None})
@user.route('/<user_id>/<username>')
def show(user_id, username):
    pass

But I guess that you want to write a single route and mark username as optional? If that's the case, I don't think it's possible.

Audrius Kažukauskas
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  • Any problems using this method when referencing endpoints and url_for ? –  Jun 20 '13 at 18:05
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    Not that I know of. Even Flask [docs](http://flask.pocoo.org/docs/api/#url-route-registrations) contain similar example (you need to scroll down a bit to see it). – Audrius Kažukauskas Jun 20 '13 at 20:54
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    You can try pip install flask_optional_routes. I created a pip for the functionality you are requesting b/c I needed it as well. The code is located at: https://github.com/sudouser2010/flask_optional_routes. – sudouser2010 Mar 12 '18 at 01:57
  • upvoted! if you have multiple tabs on your home page where each one triggers something like /one /two /three /four and you want to load different content on the same page without reloading the page, should you use a single route or multiple routes? – PirateApp Jul 25 '18 at 11:00
  • @PirateApp that cannot be achieved with just Flask and is purely a frontend feature – qaisjp Jul 09 '19 at 09:26
  • Possible to seperate those 2 route into 2 funcitons? – Q. Qiao May 30 '20 at 01:45
  • This is exactly what I needed, almost verbatim – Tommy Dec 21 '21 at 01:06
227

Almost the same as Audrius cooked up some months ago, but you might find it a bit more readable with the defaults in the function head - the way you are used to with python:

@app.route('/<user_id>')
@app.route('/<user_id>/<username>')
def show(user_id, username='Anonymous'):
    return user_id + ':' + username
mogul
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    Also, the this works if `username` is not constant. `defaults=` freezes the default value in a dictionary. – kasperhj Oct 27 '14 at 18:31
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    I prefer this one. We should keep the code as clean as it could be. – Light.G Mar 21 '19 at 11:28
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    Keep in mind there is a big caveat here: if you have multiple positional arguments and not all of them optional, flask won't understand how to build the URL properly. You can get something like /page?arg=foo where it should be /foo/page . @Audrius Kažukauskas answer works in that case, but this doesn't – rgargente Nov 12 '19 at 16:08
83

If you are using Flask-Restful like me, it is also possible this way:

api.add_resource(UserAPI, '/<userId>', '/<userId>/<username>', endpoint = 'user')

a then in your Resource class:

class UserAPI(Resource):

  def get(self, userId, username=None):
    pass
skornos
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31
@user.route('/<userId>/')  # NEED '/' AFTER LINK
@user.route('/<userId>/<username>')
def show(userId, username=None):
    pass

https://flask.palletsprojects.com/en/1.1.x/quickstart/#unique-urls-redirection-behavior

Carmellose
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14
@app.route('/', defaults={'path': ''})
@app.route('/< path:path >')
def catch_all(path):
    return 'You want path: %s' % path

http://flask.pocoo.org/snippets/57/

Dušan Maďar
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Sona
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    You should add here the info from the external link because if that link will no longer be valid, your answer will be damaged. – tomab Oct 21 '15 at 09:29
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    The link is not valid anymore. Lucky us we have archive.org (https://web.archive.org/web/20190414194437/https://flask.pocoo.org/snippets/57/) – m3nda Jul 30 '20 at 10:03
14
@user.route('/<user_id>', defaults={'username': default_value})
@user.route('/<user_id>/<username>')
def show(user_id, username):
   #
   pass
aman kumar
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8

Almost the same as skornos, but with variable declarations for a more explicit answer. It can work with Flask-RESTful extension:

from flask import Flask
from flask_restful import Resource, Api

app = Flask(__name__)
api = Api(app)

class UserAPI(Resource):
    def show(userId, username=None):
    pass

api.add_resource(UserAPI, '/<userId>', '/<userId>/<username>', endpoint='user')

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

The add_resource method allows pass multiples URLs. Each one will be routed to your Resource.

alfredo
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5

I know this post is really old but I worked on a package that does this called flask_optional_routes. The code is located at: https://github.com/sudouser2010/flask_optional_routes.

from flask import Flask

from flask_optional_routes import OptionalRoutes


app = Flask(__name__)
optional = OptionalRoutes(app)

@optional.routes('/<user_id>/<user_name>?/')
def foobar(user_id, user_name=None):
    return 'it worked!'

if __name__ == "__main__":
    app.run(host='0.0.0.0', port=5000)
sudouser2010
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0

You can write as you show in example, but than you get build-error.

For fix this:

  1. print app.url_map () in you root .py
  2. you see something like:

<Rule '/<userId>/<username>' (HEAD, POST, OPTIONS, GET) -> user.show_0>

and

<Rule '/<userId>' (HEAD, POST, OPTIONS, GET) -> .show_1>

  1. than in template you can {{ url_for('.show_0', args) }} and {{ url_for('.show_1', args) }}
lov3catch
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-8

Since Flask 0.10 you can`t add multiple routes to one endpoint. But you can add fake endpoint

@user.route('/<userId>')
def show(userId):
   return show_with_username(userId)

@user.route('/<userId>/<username>')
def show_with_username(userId,username=None):
   pass
Sergey Bargamon
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    What? Using flask 0.10.1 here and I can add multiple routes to one endpoint just fine. – jaapz Aug 04 '14 at 09:55
-9

I think you can use Blueprint and that's will make ur code look better and neatly.

example:

from flask import Blueprint

bp = Blueprint(__name__, "example")

@bp.route("/example", methods=["POST"])
def example(self):
   print("example")
Def Putra
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