Hello. I noticed the following behaviour while working with xmlrpc proxy methods.>>> import inspect, xmlrpc.client>>> proxy = xmlrpc.client.ServerProxy('http://localhost:8000')>>> proxy.mul<xmlrpc.client._Method object at 0x03B0C890>>>> inspect.signature(proxy.mul)<xmlrpc.client._Method object at 0x03B0CC90>>>>Now, according to the documentation, inspect.signature should return a signature or fail, but in this case it returns the actual object, which is misleading at least. This happens because _Method implements a proxy __getattr__, any accessed attribute becoming again a _Method. At the same time, inspect.signature happily uses try:   obj.__signature__except AttributeError:   ...to obtain the signature, if present.The attached patch checks if __signature__ is an actual Signature object. I searched, but couldn't find any, if __signature__ can be anything, so I hope that this approach works.

This behaviour is indeed a bug. However, I think that the solution you propose is wrong.If we ignore invalid contents of __signature__ we are masking a bug or incorrect behaviour. In this case, you should have checked the requested attribute name in '__getattr__', and return something other than _Method, if it is a '__signature__'.Please find attached a patch, that checks if __signature__ is an instance of Signature class, and raises a TypeError if it isn't.

Your patch looks good to me.

New changesetcc0f5d6ccb70 by Yury Selivanov in branch '3.4':inspect: Validate that __signature__ is None or an instance of Signature.http://hg.python.org/cpython/rev/cc0f5d6ccb70New changesetfa5b985f0920 by Yury Selivanov in branch 'default':inspect: Validate that __signature__ is None or an instance of Signature.http://hg.python.org/cpython/rev/fa5b985f0920

Fixed in 3.4 and 3.5.Thanks for the bug report!