collections_wrapper_2.py

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


COLLECTION_PROXY_METHODS = ('__getitem__', '__setitem__', '__len__', '__repr__')
LIST_PROXY_METHODS = COLLECTION_PROXY_METHODS + ('append',)
DICT_PROXY_METHODS = COLLECTION_PROXY_METHODS + ()

def assertion(condition, message):
    if not condition:
        raise AssertionError(message)

def proxy(name):
    def wrapper(self, *args, **kwargs):
        return getattr(self._obj, name)(*args, **kwargs)
    return wrapper        

def create_collections_wrapper(assertion_f=None, list_index_suffix='_', dict_keys_suffix='_'):

    if assertion_f is None:
        assertion_f = assertion

    def get_data_from_dict(self, name):
        alt_name = name
        obj = self._obj
        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_data_from_list(self, name):
        obj = self._obj
        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 BaseCollectionWrapper(object):
    
        def __init__(self, obj):
            self._obj = obj
        
        def __getattr__(self, name):    
            return wrap(self._get_data(name))
    
    DictWrapper = type('DictWrapper', (BaseCollectionWrapper,), dict(
        _get_data=get_data_from_dict,
        **{method: proxy(method) for method in DICT_PROXY_METHODS}
    ))
    ListWrapper = type('ListWrapper', (BaseCollectionWrapper,), dict(
        _get_data=get_data_from_list,
        **{method: proxy(method) for method in LIST_PROXY_METHODS}
    ))
    
    def wrap(obj):
        if isinstance(obj, dict):
            return DictWrapper(obj)
        elif isinstance(obj, list):
            return ListWrapper(obj)
        else:
            return obj
        
    return wrap

    
w = create_collections_wrapper()(test)
print w._objects._1.bar