CDN URL

can_url_for.py

from flask import Flask, url_for
from werkzeug.urls import url_encode


app = Flask(__name__)


def cdn_url_builder(error, endpoint, values):
    if endpoint != 'cdn':
        return
    filename = values.pop('filename')
    # Ignore _external flag, we're always external
    values.pop('_external', None)
    return 'http://mycdn.invalid/%s/%s/%s%s' % (
        filename[:1],
        filename[:2],
        filename,
        values and '?' + url_encode(values) or '',
    )


app.url_build_error_handlers.append(cdn_url_builder)


@app.route('/')
def index():
    return url_for('cdn', filename='foobar.png')


print app.test_client().get('/').data
Running this returns:

# http://mycdn.invalid/f/fo/foobar.png