python - How to inherit a class attribute that is a dict and make it unique? -

this works expected;

class foo(object):     name = ''  class bar1(foo):     pass  class bar2(foo):     pass  bar1.name == bar2.name # returns true bar1.name = 'bar1' bar1.name == bar2.name # returns false, want. 

this doesn't work same, want to;

class foo(object):     fields = {'name':''}  class bar1(foo):     pass  class bar2(foo):     pass  bar1.fields['name'] == bar2.fields['name'] # returns true bar1.fields['name'] = 'bar1' bar1.fields['name'] == bar2.fields['name'] # returns true, isn't want. 

it seems subclasses still pointing @ same dict object specified in main class, want them have unique dicts. how can without writing fields = {'name':''} in each of subclasses?

ps- want use class level attributes, not instance attributes, of instances create use 'shared' dict.

the simplest way using meta-class (i've assumed python 2.x syntax):

class fieldsmeta(type):      def __new__(mcs, name, bases, dict):         """this controls creation of each new class."""         dict.update(fields={'name': ''})         return type.__new__(mcs, name, bases, dict)   class parent(object):     __metaclass__ = fieldsmeta   class child(parent):     pass 

in use:

>>> parent.fields {'name': ''} >>> child.fields {'name': ''} >>> child.fields parent.fields false >>> child.fields['name'] = 'child' >>> child.fields {'name': 'child'} >>> parent.fields {'name': ''} 

see e.g. data-model documentation __new__:

[__new__] commonly overridden in custom metaclasses in order customize class creation.

and section on customizing class creation.