@app.route('/double/<int:number>')
def double(number):
    return '%d' % (number * 2)

class UserConverter(BaseConverter):
    """Converts Users for flask URLs."""

    def to_python(self, value):
        """Called to convert a `value` to its python equivalent.

        Here, we convert `value` to a User.
        """
        # Anytime an invalid value is provided, raise ValidationError.  Flask
        # will catch this, and continue searching the other routes.  First,
        # check that value is an integer, if not there is no way it could be
        # a user.
        if not value.isdigit():
            raise ValidationError()
        user_id = int(value)

        # Look up the user in the database.
        if user_id not in _database:
            raise ValidationError()

        # Otherwise, return the user.
        return _database[user_id]

    def to_url(self, value):
        """Called to convert a `value` to its `url` equivalent.

        Here we convert `value`, the User object to an integer - the user id.
        """
        return str(value.id)

app.url_map.converters['user'] = UserConverter

url_for('find_user', user=user)

from flask import Flask, url_for
from werkzeug.routing import BaseConverter, ValidationError


class User:

    def __init__(self, id, name):
        self.id = id
        self.name = name


class UserConverter(BaseConverter):
    """Converts Users for flask URLs."""

    def to_python(self, value):
        """Called to convert a `value` to its python equivalent.

        Here, we convert `value` to a User.
        """
        # Anytime an invalid value is provided, raise ValidationError.  Flask
        # will catch this, and continue searching the other routes.  First,
        # check that value is an integer, if not there is no way it could be
        # a user.
        if not value.isdigit():
            raise ValidationError()
        user_id = int(value)

        # Look up the user in the database.
        if user_id not in _database:
            raise ValidationError()

        # Otherwise, return the user.
        return _database[user_id]

    def to_url(self, value):
        """Called to convert a `value` to its `url` equivalent.

        Here we convert `value`, the User object to an integer - the user id.
        """
        return str(value.id)


# Create a `database` of users.
_database = {
    1: User(1, 'Bob'),
    2: User(2, 'Jim'),
    3: User(3, 'Ben')
}

app = Flask(__name__)
app.url_map.converters['user'] = UserConverter

@app.route('/find/<user:user>')
def find_user(user):
    return "User: %s" % user.name

@app.route('/find/<user:user>/extrapath')
def find_userextra(user):
    return 'User extra: %s' % user.name

@app.route('/users')
def list_users():
    # Return some broken HTML showing url's to our users.
    s = ''
    for user in _database.values():
        s += url_for('find_user', user=user) + '<br/>'
    return s

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

@app.route('/user/<user:user>/something')

@app.route('/user/<user:user>/something-else')

@app.route('/user/<user:user>/)