Why isn't this classprop implementation working?
Based on a question I previously asked, I tried to come up with a class property that would allow setting as well as getting. So I wrote this and put it in a module util
:
class classprop(object):
def __init__(self, fget, fset=None):
if isinstance(fget, classmethod):
self.fget = fget
else:
self.fget = classmethod(fget)
if not fset or isinstance(fset, classmethod):
self.fset = fset
else:
self.fset = classmethod(fset)
def __get__(self, *a):
return self.fget.__get__(*a)()
def __set__(self, cls, value):
print 'In __set__'
if not self.fset:
raise AttributeError, "can't set attribute"
fset = self.fset.__get__(cls)
fset(value)
class X(object):
@classmethod
def _get_x(cls):
return 1
@classmethod
def _set_x(cls, value):
print 'You set x to {0}'.format(value)
x = classprop(fget=_get_x, fset=_set_x)
While开发者_JAVA技巧 getting is working, setting doesn't seem to be getting called:
>>> util.X.x
1
>>> util.X.x = 1
>>>
What am I doing wrong?
(And I have seen implementations of this that work a bit differently. I'm specifically wanting to know why this implementation isn't working.)
The doc's say:
object.__set__(self, instance, value)
Called to set the attribute on an instance instance of the owner class to a new value, value.
Unlike for __get__
, it does not mention class attributes. So Python won't call any __set__
on a class attribute.
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