simplest possible url-rewriting middleware example.py

class rewrite(object):
    def __init__(self, real_app):
        self.real_app = real_app
    def __call__(self, environ, start_response):
        if environ.get('PATH_INFO', '') == 'old_url':
            environ['PATH_INFO'] = 'new_url'
        return self.real_app(environ, start_response)

from myapp import wsgi_app
from myserver import serve

serve(rewrite(wsgi_app))