New submission from mike bayer:
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)
----------
messages: 212313
nosy: zzzeek
priority: normal
severity: normal
status: open
title: inspect.getargspec() returns wrong answer with property.__delete__()
versions: Python 3.4
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Python tracker <rep...@bugs.python.org>
<http://bugs.python.org/issue20786>
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