The decorator named 'node' takes mapping and call next wsgi apprication. The mapping's key is URL pattern you want to match, and the value is a name for a function which will be called when the key pattern matches to URL. In this example, '/a/' calls node2, '/b/' calls node3, '/' calls node1 and '/b/a/' calls node1 too.

nodechain.py

from wsgiref.simple_server import make_server

from webob.dec import wsgify

def node(mapping):
    def deco(func):
        def wrapper(request):
            try:
                called_count = request.environ['nodechain.chaincount']
            except KeyError:
                called_count = 0
            node_name = request.path_info.split('/')[called_count+1] # /a/b/c => a
            node = mapping.get(node_name)
            if not node:
                node = func
            else:
                from os.path import basename, splitext
                name, _ = splitext(basename(__file__))
                mod = __import__(name)
                if hasattr(mod, node):
                    node = getattr(mod, node)
                else:
                    node = func
            try:
                request.environ['nodechain.chaincount'] += 1
            except KeyError:
                request.environ['nodechain.chaincount'] = 1
            response = node(request)
            return response
        return wrapper
    return deco


@wsgify
def node2(request):
    return "OK. I'm node2"


@wsgify
@node({'a': 'node1', 'b': 'node2'})
def node3(request):
    return "OK. I'm node3"


@wsgify
@node({'a': 'node2', 'b': 'node3'})
def node1(request):
    return "OK. I'm node1"


if __name__ == '__main__':
    httpd = make_server('', 8080, node1)
    httpd.serve_forever()