Notice that Peter's approach also works without inheritance:
registries = {}
@property
def per_class(self):
cls = type(self)
try:
return registries[cls]
except KeyError:
result = registries[cls] = []
return result
class A(object): per_class=per_class
class B(object): per_class=per_class
assert A().per_class is A().per_class
assert B().per_class is B().per_class
assert A().per_class is not B().per_class
(you can also put the per_class property in a module and import it
with
class A(object): from module import per_class).
There is no need to use inheritance if you only need one method.
Notice also that if you
are working with a complex third party framework (say Django) that may
use metaclasses
or strange tricks (such as __slots__) the safer way is to avoid both
inheritance and metaclasses.
HTH,
Michele
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