Not quite sure this is a bug, but the problem caused me 
considerable time to track down (Python 2.3.2 on Solaris).

assume proxy is a variable for a server proxy created with
xmlrpclib.Server(), but sometimes it is None (assume a
default argument to a function).

The comparisons

if proxy != None:

or

if proxy:

fail with (to me) rather incomprehensible error messages.

However, the test

if proxy is not None:

does what I expect.

Is this a feature or a bug?


Thanks a lot for looking into it.

Andreas Eisele

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I also encountered the same bug. It appears that the
ServerProxy class does not implement the necessary operator
methods and therefore the defined __getattr__ method takes
over and gets it wrong. 

Adding the following methods to ServerProxy resolves the issue:

    def __eq__(self, other):
        return self is other
        
    def __ne__(self, other):
        return self is not other
        
    def __nonzero__(self):
        return True

It would be great, if this could be fixed in xmlrpclib.

Thanks,
  Gerhard Reitmayr

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Note that comparisons to None are better written as 'if
proxy is not None'; they're faster that way.

There's a more general problem here: any Python special
methods are forwarded via XML-RPC, so if you write 'proxy +
5', it tries to call __coerce__ and fails; if you write
'proxy[5]', it calls __getitem__ and fails.

One fix would be to implement all of these methods on
ServerProxy.  Another would be to ignore methods beginning
and ending with '__' in the __getattr__, but then you
couldn't call such methods at all.  

I suggest that there's really nothing to do here; if you try
certain operations on a ServerProxy, they'll fail.  Closing
as "won't fix".