merger.py

import inspect
import operator


#
# Core mechanic
#

def merge_from_ancestors(self, attribute):
    """
    Merge parent, etc class' <attribute> list values into one list.

    Walks from top to bottom; mildly pointless with lists, more useful for a
    dict-using implementation perhaps.
    """
    return reduce(
        operator.add,
        map(
            lambda x: getattr(x, attribute, []),
            list(reversed(inspect.getmro(self.__class__)))
        ),
        []
    )


#
# Super explicit 1st version
#

class Merger(object):
    def get_values(self):
        return merge_from_ancestors(self, 'values')

class Parent(Merger):
    values = ['foo', 'bar']

class Child(Parent):
    values = ['biz', 'baz']

print Child().get_values() # => ['foo', 'bar', 'biz', 'baz']


#
# Slightly fancier/more implicit
#

class Merger(object):
    @property
    def values(self):
        return merge_from_ancestors(self, '_values')

class Parent(Merger):
    _values = ['foo', 'bar']

class Child(Parent):
    _values = ['biz', 'baz']

print Child().values # => ['foo', 'bar', 'biz', 'baz']