Python lazy initialization mixin and decorator

lazy_init.py

""" Provides a base class that allows lazy initialization
"""

from functools import update_wrapper


class LazyInit(object):
    _wrapped_object = None
    _wrapped_object_base = None
    _wrapped_object_initialized = False
    # List of attributes to pass through to object.__getattribute__. We know they are set and should resolve to the
    # LazyInit class.
    attribute_whitelist = (
        '__dict__',
        '_wrapped_object',
        '_wrapped_object_base',
        '_wrapped_object_initialized',
        '_wrapped_object_init',
        'attribute_whitelist',
    )


    @staticmethod
    def _wrapped_object_init(obj):
        raise NotImplementedError

    # Must override __getattribute__ since we're using update_wrapper, which updates the instance's __dict__
    def __getattribute__(self, name):
        whitelist = object.__getattribute__(self, 'attribute_whitelist')
        if name in whitelist:
            return object.__getattribute__(self, name)
        if not self._wrapped_object_initialized:
            init, object_base = self._wrapped_object_init, self._wrapped_object_base
            self._wrapped_object = init(object_base)
            update_wrapper(self, self._wrapped_object, assigned=('__module__', '__doc__'))
            self._wrapped_object_initialized = True
        return getattr(self._wrapped_object, name)


def lazy_init(obj, init):
    class Stub(LazyInit):
        _wrapped_object_base = obj
        _wrapped_object_init = staticmethod(init)

    return update_wrapper(Stub(), obj)