Can Flask have optional URL parameters?

Question

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?

Babbitt

Answer 1

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.

Hershberger

Any problems using this method when referencing endpoints and url_for ? – Willianwillie

Not that I know of. Even Flask docs contain similar example (you need to scroll down a bit to see it). – Kopaz

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: github.com/sudouser2010/flask_optional_routes. – Anthelion

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? – Antenatal

@Antenatal that cannot be achieved with just Flask and is purely a frontend feature – Embodiment

Possible to seperate those 2 route into 2 funcitons? – Racklin

This is exactly what I needed, almost verbatim – Newsprint

@user.route('/<user_id>/<username>') In this Application username is string . Like if I want to use bool(either True/False) in place of username, How is it to change – Libertylibia

This is generally OK, however it leaves you with potential for 308's to be returned when you pass in the default route param as part of the call (eg: if your username default were to be say "anonymous" and you pass that value in, you'd get a 308 redirecting to the route without a param instead of just getting a normal response back) – Launalaunce

A better approach is @mogul answer below (see my comment above for why this answer isn't the best) – Launalaunce

Answer 2

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

Ebberta

Also, the this works if username is not constant. defaults= freezes the default value in a dictionary. – Sweatbox

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 – Buckwheat

This also prevents flask redirecting with 308's when you omit the optional URI path param. ie if you use the defaults= approach with your above default value, and then specify as part of the URI the same Anonymous string as the username optional arg, you will get a 308 bouncing you to /<user_id> – Launalaunce

Answer 3

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

Foolery

Answer 4

@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

Wyn

Answer 5

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

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

Trolley

You should add here the info from the external link because if that link will no longer be valid, your answer will be damaged. – Love

The link is not valid anymore. Lucky us we have archive.org (web.archive.org/web/20190414194437/https://flask.pocoo.org/…) – Paramour

Answer 6

@user.route('/<user_id>', defaults={'username': default_value})
@user.route('/<user_id>/<username>')
def show(user_id, username):
   #
   pass

Duffie

Answer 7

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.

Dynah

Answer 8

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)

Anthelion

Answer 9

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>

3. than in template you can {{ url_for('.show_0', args) }} and {{ url_for('.show_1', args) }}

Spherule

Answer 10

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

Avian

What? Using flask 0.10.1 here and I can add multiple routes to one endpoint just fine. – Coincidentally

Answer 11

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")

Ml

This does not answer the question. – Booker