collections_wrapper.py

test = dict(
    len=1,
    objects=[
        dict(foo='bar'),
        dict(bar='baz'),
    ],
    sub_object=dict(foo='bar')
)


def create_wrapper(assertion_f=None, list_index_suffix='_', dict_keys_suffix='_'):
    
    def assertion(condition, message):
        if not condition:
            raise AssertionError(message)

    if assertion_f is None:
        assertion_f = assertion
            
    def get_from_dict(obj, name):
        alt_name = name
        if name.startswith(dict_keys_suffix):
            alt_name = name[len(dict_keys_suffix):]
        assertion_f(name in obj or alt_name in obj, "key '{}' not found".format(name))
        return obj.get(alt_name, obj.get(name))

    def get_from_list(obj, name):
        assertion_f(name.startswith(list_index_suffix), "list index should start with '{}'".format(list_index_suffix))
        index = name[len(list_index_suffix):]
        assertion_f(index.isdigit(), 'list index should be digit, not {}'.format(index))
        index = int(index)
        assertion_f(index < len(obj), "index {} is out of range ({})".format(index, len(obj)))
        return obj[index]

    class CollectionsWrapperMixin:

        def __getattr__(self, name):
            value = None

            if isinstance(self, dict):
                value = get_from_dict(self, name)
            elif isinstance(self, list):
                value = get_from_list(self, name)

            if isinstance(value, dict):
                value = wrappedDict(value)
            elif isinstance(value, list):
                value = wrappedList(value)

            return value

    wrappedDict = type('wrappedDict', (dict, CollectionsWrapperMixin), {})
    wrappedList = type('wrappedList', (list, CollectionsWrapperMixin), {})
    
    def wrap(obj):
        if isinstance(obj, dict):
            return wrappedDict(obj)
        elif isinstance(obj, list):
            return wrappedList(obj)
        else:
            raise Exception('object {} can not be wrapped'.format(obj))
    return wrap
    
w = create_wrapper()(test)
print w.objects._1