Re: [Python-ideas] Callable properties

7 Jun 2010


      On Mon, Jun 7, 2010 at 5:46 PM, Ian Bicking  wrote:
...
On Mon, Jun 7, 2010 at 5:51 AM, George Sakkis 
wrote:
...
I'm wondering if there is any downside in making properties callable:
class callableproperty(property):
   def __call__(self, obj):
       return self.fget(obj)
class Foo(object):
   @property
   def bar(self):
       return self
   @callableproperty
   def baz(self):
       return self
...
...
...
foo = Foo()
foo.baz is Foo.baz(foo)
True
foo.bar is Foo.bar(foo)
...
TypeError: 'property' object is not callable
As for the motivation, having callable properties would make it easier
to stack them with other decorators that typically expect callables.
Am I missing something ?
I find stacking descriptors to be easier than it might at first appear (and
making decorators descriptors is also advantageous).  Treating properties
like Yet Another Descriptor helps here.  As it is you could use
Foo.bar.__get__(foo), or generally Foo.bar.__get__ as a callable.
The problem though is that most existing decorators expect their input
to be a function or a callable at best, not a descriptor; they have to
do something like ``func = getattr(func, '__get__', func)`` to cover
all cases. But regardless, I'm not proposing to make all descriptors
callable (it probably doesn't make sense in general), just properties.

George