property using a classmethod

[Lie Ryan]

Emanuele D'Arrigo wrote:
> Greetings,
> 
> today I did something like this:
> 
> class MyClass(object):
> 
>     @classmethod
>     def myClassMethod(self):
>          print "ham"
> 
>      myProperty = property(myClassMethod, None, None)
> 
> As many of you know this doesn't work and returns a TypeError: the
> object passed to the property is not a callable function but a
> classmethod object, which isn't callable at all.

That code runs fine for me. Although I doubt the behavior is what you
wanted to do.

> So, how do I do this?
> Ultimately all I want is a non-callable class-level attribute
> MyClass.myProperty that gives the result of MyClass.myClassMethod().

This works like what you seem to want (it's ugly):

class MyClass(object):
    class _MyClass(object):
        @classmethod
        def myClassMethod(cls):
            return 'ham'
        @property
        def myProperty(self):
            return MyClass._MyClass.myClassMethod()
    @classmethod
    def myClassMethod(cls):
        return MyClass._MyClass.myClassMethod()
    @property
    def myProperty(self):
        return MyClass._MyClass.myClassMethod()

    def __call__(self, *args, **kargs):
        # this is __init__
        return MyClass._MyClass(*args, **kargs)
# note this is NOT a real MyClass instantiation
MyClass = MyClass()

$ python -i ./strangeclass.py
>>> MyClass.myClassMethod()
'ham'
>>> MyClass.myProperty
'ham'
>>> mc = MyClass()
>>> mc.myProperty
'ham'
>>> mc.myClassMethod()
'ham'