New submission from Alexey Muranov <alexey.mura...@gmail.com>:
I expect that overriding methods with themselves like in the following example
should not change the behaviour of the class:
class C:
a = 1
def __init__(self, b):
self.b = b
def f(self, x):
return x*self.a + self.b + 1
@classmethod
def g(cls, y):
return y*cls.a + 2
@staticmethod
def h(z):
return z + 3
class D(C):
def f(self, *args, **kwargs):
return super(__class__, self).f(*args, **kwargs)
@classmethod
def g(cls, *args, **kwargs):
return super(__class__, cls).g(*args, **kwargs)
@staticmethod
def h(*args, **kwargs):
return super(__class__, __class__).h(*args, **kwargs)
c = C(7)
d = D(7)
assert c.f(42) == d.f(42)
assert c.g(42) == d.g(42)
assert c.h(42) == d.h(42)
(Moreover, I expect to be able to extend superclass method this way.)
However, this does not work with `__new__`:
class C:
def __init__(self, x):
self.x = x
print(x)
class D(C):
@staticmethod
def __new__(*args, **kwargs):
return super(__class__, __class__).__new__(*args, **kwargs)
C(7) # fine
D(7) # TypeError: object.__new__() takes exactly one argument
I think this is not a desirable feature. I would call it a bug.
By the way, I understand why `object`'s `__init__` can complain about a wrong
number of arguments, but I do not see a point in making `object`'s `__new__`
complain about it.
Here is my current workaround:
class T:
@staticmethod
def __new__(cls, *_args, **_kwargs):
return object.__new__(cls)
class E(C, T):
@staticmethod
def __new__(*args, **kwargs):
return super(__class__, __class__).__new__(*args, **kwargs)
C(42) # fine
E(42) # fine
A possibly related issue: #32768 (https://bugs.python.org/issue32768)
----------
components: Interpreter Core
messages: 341705
nosy: alexey-muranov
priority: normal
severity: normal
status: open
title: Overriding __new__ method with itself changes behaviour of the class
type: behavior
versions: Python 3.7, Python 3.8
_______________________________________
Python tracker <rep...@bugs.python.org>
<https://bugs.python.org/issue36827>
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