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The Python builtin property() historically does not allow inspect.getargspec to be called on any of __get__(), __set__(), or __delete__(). As of 3.4, it seems that this call now succeeds. However the answer it gives for __delete__() seems to be incorrect. Below illustrates that property.__delete__() accepts two arguments "self" and "instance" but inspect is giving a misleading answer:
import inspect
# userland descriptor
class Descriptor(object):
 def __get__(self, instance, owner):
 if instance is None:
 return self
 def __set__(self, instance, value):
 pass
 def __delete__(self, instance):
 pass
# class with property + userland descriptor
class X(object):
 @property
 def foo(self):
 pass
 @foo.deleter
 def foo(self):
 pass
 bar = Descriptor()
# property.__delete__ and Descriptor.__delete__ both accept two arguments:
property.__delete__(X.foo, X())
Descriptor.__delete__(X.bar, X())
# on all versions, userland __delete__ produces 'self', 'instance' for args
assert inspect.getargspec(Descriptor.__delete__) == (['self', 'instance'], None, None, None)
try:
 # but on python 3.4, it returns ['instance']
 insp = inspect.getargspec(property.__delete__)
 assert insp == (['self', 'instance'], None, None, None), insp
except TypeError as e:
 # on all other python versions, raises
 # <slot wrapper '__delete__' of 'property' objects> is not a Python function
 print("Exception: %s" % e)