[Python-Dev] Evil isinstance() (original) (raw)

Brian Quinlan brian@sweetapp.com
Mon, 1 Apr 2002 18:01:03 -0800

Guido wrote: [xmlrpclib creates attributes on demand]

Hm. I didn't know xmlrpc did that, and I think it's pretty unique in this respect.

I've seen other RPC code do this. Some soaplib? objects used to infinitely recurse, if you repred, them due to a subtle getattr bug.

It looks like a hack, and one that can only work as long as attributes on xmlrpc instances are always supposed to be methods.

I imagine that we are talking about xmlrpclib.Server. This class creates callable objects, representing remote method calls, when attributes are requested. This allows for a pretty natural method call syntax e.g.

server = xmlrpclib.Server('http://...')
server.do_something_remote() server.do_something_else()

XML-RPC does not have an attribute concept.

Why didn't you choose to special-case xmlrpc? It appears that introspecting an xmlrpc instance is hopeless anyway... (Depending on what you need the introspection for, of course. You haven't told us the whole story.)

It's not necessarily hopeless but getting a list of available methods (and therefore attribute that should be offered) costs a round-trip and isn't supported by all XML-RPC servers (like Python's SimpleXMLRPCServer, for example).

Cheers, Brian