import inspect


def build_from_registry(cfg, registry, default_args=None):
    """Build a module from config dict.
    Args:
        cfg (dict): Config dict. It should at least contain the key "type".
        registry (:obj:`Registry`): The registry to search the type from.
        default_args (dict, optional): Default initialization arguments.
    Returns:
        obj: The constructed object.
    """
    assert isinstance(cfg, dict) and 'type' in cfg
    assert isinstance(default_args, dict) or default_args is None
    args = cfg.copy()
    obj_type = args.pop('type')
    if isinstance(obj_type, str):
        obj_cls = registry.get(obj_type)
        if obj_cls is None:
            raise KeyError('{} is not in the {} registry'.format(
                obj_type, registry.name))
    elif inspect.isclass(obj_type):
        obj_cls = obj_type
    else:
        raise TypeError('type must be a str or valid type, but got {}'.format(
            type(obj_type)))
    if default_args is not None:
        for name, value in default_args.items():
            args.setdefault(name, value)
    return obj_cls(**args)