[Twisted-Python] Monitoring configuration of twisted calls.

[Jean-Paul Calderone]

On Thu, 28 Aug 2008 10:22:01 -0700 (PDT), Steve Lewis <spiritualmechanic at yahoo.com> wrote:
>Okay, that seems to work. One more question:
>
>We've defined a class called XMLRPCWithRemote that subclasses XMLRPC. Some of the methods are local, others with be called using the Proxy. I tried to wrap the function but I'm getting:
>
>exceptions.AttributeError: Deferred instance has no __call__ method
>
>
>This is the code I have for wrapping:
>
>              def wrapper(*args, **kw):
>                        func = self._getProxy(URL["url"], URL["user"], URL["passwd"]).callRemote(remote_method, *args, **kw)
>                        result = func(*args, **kw)
>                        monitor[functionPath] = True
>
>                        return result
>
>                    return wrapper
>
>_getProxy is defined thusly:
>
>    def _getProxy(self, url, username=None, password=None):
>        log.msg("Get proxy")
>        return Proxy(url, user=username, password=password, allowNone=True, useDateTime=True)
>
>
>So it looks like I'm getting a deferred back from the callRemote, so it appears harder to wrap? I think that's what's going on. I'm guessing the local method doesn't require a deferred, so that's why it works.
>
>Is there something obvious I'm missing? I started going down the path of overriding xmlrpc.Proxy or xmlrpc._QueryFactory but I'm not sure that's the simplest way.

The wrapper I gave as an example doesn't handle Deferreds, indeed.  Have
you worked with Deferreds before?  If not, you may want to read some of
the documentation about them, eg:

 http://twistedmatrix.com/projects/core/documentation/howto/defer.html

That aside, I don't really understand the modifications you've made.  It
seems that you're doing an XML-RPC call to get a function object to call
to produce a result to give to the XML-RPC client which made a call on to
you.  Since XML-RPC calls can't result in functions, I don't understand
this.

Jean-Paul