Is there any way to create a class property in Python?

Question

The following doesn\'t work for some reason:

>>> class foo(object):
...     @property
...     @classmethod
...     def bar(cls):
...             ret         


        

Answer 1

If you want the descriptor property to trigger when you get an attribute from object X, then you must put the descriptor in type(X). So if X is a class, the descriptor must go in the class's type, also known as the class's metaclass -- no "trickery" involved, it's just a matter of completely general rules.

Alternatively, you might write your own special-purpose descriptor. See here for an excellent "how-to" treaty on descriptors. Edit for example:

class classprop(object):
  def __init__(self, f):
    self.f = classmethod(f)
  def __get__(self, *a):
    return self.f.__get__(*a)()

class buh(object):
  @classprop
  def bah(cls): return 23

print buh.bah

emits 23, as desired.