strange behaviour of xmlrpclib.Server proxy

[eisele]

BPO	901198
Nosy	@akuchling

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = 'https://github.com/akuchling'
closed_at = <Date 2005-12-04.17:26:27.000>
created_at = <Date 2004-02-20.16:47:36.000>
labels = ['library']
title = 'strange behaviour of xmlrpclib.Server proxy'
updated_at = <Date 2005-12-04.17:26:27.000>
user = 'https://bugs.python.org/eisele'

bugs.python.org fields:

activity = <Date 2005-12-04.17:26:27.000>
actor = 'akuchling'
assignee = 'akuchling'
closed = True
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2004-02-20.16:47:36.000>
creator = 'eisele'
dependencies = []
files = []
hgrepos = []
issue_num = 901198
keywords = []
message_count = 3.0
messages = ['20077', '20078', '20079']
nosy_count = 3.0
nosy_names = ['akuchling', 'eisele', 'merl7n']
pr_nums = []
priority = 'normal'
resolution = 'wont fix'
stage = None
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue901198'
versions = ['Python 2.5']

[eisele]

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

[merl7n]

Logged In: YES
user_id=12764

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

[akuchling]

Logged In: YES
user_id=11375

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".