Automatic class attribute

[Franck PEREZ]

Hello all,

Considering the following code :

class C(object):
...: observers = []
...:
...: @classmethod
...: def showObservers(cls):
...: print cls.observers

class D1(C):
...: observers = [] #could it be moved in C ?

class D2(C):
...: observers = [] #could it be moved in C ?

I want each child class of C to have it's own "observers" class attribute.

The code I provided works... but I'd like to avoid typing "observers =
[]" in each child class.

Is it possible to define something in C which would basically mean :
"for each child class, automatically bind a new list attribute called
observers" ?

Are metaclasses a way ? Is it possible to avoid them ?
Thanks a lot,
Franck

 

[Kirk McDonald]

Hello all,

Considering the following code :

class C(object):
...: observers = []
...:
...: @classmethod
...: def showObservers(cls):
...: print cls.observers

class D1(C):
...: observers = [] #could it be moved in C ?

class D2(C):
...: observers = [] #could it be moved in C ?

I want each child class of C to have it's own "observers" class attribute.

The code I provided works... but I'd like to avoid typing "observers =
[]" in each child class.

Is it possible to define something in C which would basically mean :
"for each child class, automatically bind a new list attribute called
observers" ?

Are metaclasses a way ? Is it possible to avoid them ?
Thanks a lot,
Franck

By an astounding coincidence, I was just working on a similar problem.
Metaclasses can do this, no problem:

class M(type):
def __init__(cls, name, bases, dict):
cls.observers = []

def showObservers(cls):
print cls.observers

class C(object):
__metaclass__ = M

class D1(C): pass
class D2(C): pass

-Kirk McDonald

 

[Franck PEREZ]

Hello all,

Considering the following code :

class C(object):
...: observers = []
...:
...: @classmethod
...: def showObservers(cls):
...: print cls.observers

class D1(C):
...: observers = [] #could it be moved in C ?

class D2(C):
...: observers = [] #could it be moved in C ?

I want each child class of C to have it's own "observers" class attribute.

The code I provided works... but I'd like to avoid typing "observers =
[]" in each child class.

Is it possible to define something in C which would basically mean :
"for each child class, automatically bind a new list attribute called
observers" ?

Are metaclasses a way ? Is it possible to avoid them ?
Thanks a lot,
Franck

By an astounding coincidence, I was just working on a similar problem.
Metaclasses can do this, no problem:

class M(type):
def __init__(cls, name, bases, dict):
cls.observers = []

def showObservers(cls):
print cls.observers

class C(object):
__metaclass__ = M

class D1(C): pass
class D2(C): pass

-Kirk McDonald

Works great. Thanks a lot.