example of subclassing flask.Flask to change the strict_slashes default to False for url routing

laxflask.py

import flask

class LaxFlask(flask.Flask):
    def add_url_rule(self, *args, **kwargs):
        if 'strict_slashes' not in kwargs:
            kwargs['strict_slashes'] = False
        super(LaxFlask, self).add_url_rule(*args, **kwargs)

# instantiate with LaxFlask instead of Flask
app = LaxFlask(..)

And of course thanks to @wilsaj as well!