Question

I’m trying to write a library that will register an arbitrary list of service calls from multiple service endpoints to a container. I intend to implement the service calls in classes written one per service. Is there a way to maintain the boundedness of the methods from the service classes when registering them to the container (so they will still have access to the instance data of their owning object instance), or must I register the whole object then write some sort of pass through in the container class with __getattr__ or some such to access the methods within instance context?

container:

class ServiceCalls(object):
    def __init__(self):
        self._service_calls = {}
    def register_call(self, name, call):
        if name not in self._service_calls:
            self._service_calls[name] = call
    def __getattr__(self, name):
        if name in self._service_calls:
           return self._service_calls[name]

services:

class FooSvc(object):
    def __init__(self, endpoint):
        self.endpoint = endpoint
    def fooize(self, *args, **kwargs):
        #call fooize service call with args/kwargs utilizing self.endpoint
    def fooify(self, *args, **kwargs):
        #call fooify service call with args/kwargs utilizing self.endpoint


class BarSvc(object):
    def __init__(self, endpoint):
        self.endpoint = endpoint
    def barize(self, *args, **kwargs):
        #call barize service call with args/kwargs utilizing self.endpoint
    def barify(self, *args, **kwargs):
        #call barify service call with args/kwargs utilizing self.endpoint

implementation code:

foosvc = FooSvc('fooendpoint')
barsvc = BarSvc('barendpoint')
calls = ServiceCalls()
calls.register('fooize', foosvc.fooize)
calls.register('fooify', foosvc.fooify)
calls.register('barize', barsvc.barize)
calls.register('barify', barsvc.barify)
calls.fooize(args)

Answer 1

What you are trying to do will work fine, as you can see by running your own code. 🙂

The object foosvc.fooize is called a “bound method” in Python, and it contains both, a reference to foosvc and to the function FooSvc.fooize. If you call the bound method, the reference to self will be passed implicitly as the first paramater.

On a side note, __getattr__() shouldn’t silently return None for invalid attribute names. Better use this:

def __getattr__(self, name):
    try:
        return self._service_calls[name]
    except KeyError:
        raise AttributeError