objproxies.py

import sys

if sys.version_info.major < 3:
    raise ImportError(
            'objproxies requires Python 3. For Python 2, refer to ProxyTypes '
            '<http://cheeseshop.python.org/pypi/ProxyTypes>')


class AbstractProxy(object):
    """Delegates all operations (except ``.__subject__``) to another object"""
    __slots__ = ()

    def __call__(self, *args, **kw):
        return self.__subject__(*args, **kw)

    def __getattribute__(self, attr, oga=object.__getattribute__):
        subject = oga(self, '__subject__')
        if attr == '__subject__':
            return subject
        return getattr(subject, attr)

    def __setattr__(self, attr, val, osa=object.__setattr__):
        if attr == '__subject__':
            osa(self, attr, val)
        else:
            setattr(self.__subject__, attr, val)

    def __delattr__(self, attr, oda=object.__delattr__):
        if attr == '__subject__':
            oda(self, attr)
        else:
            delattr(self.__subject__, attr)

    def __bool__(self):
        return bool(self.__subject__)

    def __getitem__(self, arg):
        return self.__subject__[arg]

    def __setitem__(self, arg, val):
        self.__subject__[arg] = val

    def __delitem__(self, arg):
        del self.__subject__[arg]

    def __getslice__(self, i, j):
        return self.__subject__[i:j]

    def __setslice__(self, i, j, val):
        self.__subject__[i:j] = val

    def __delslice__(self, i, j):
        del self.__subject__[i:j]

    def __contains__(self, ob):
        return ob in self.__subject__

    for name in 'repr str hash len abs complex int long float iter'.split():
        exec("def __%s__(self): return %s(self.__subject__)" % (name, name))

    for name in 'cmp', 'coerce', 'divmod':
        exec("def __%s__(self, ob): return %s(self.__subject__, ob)" % (name, name))

    for name, op in [
        ('lt', '<'), ('gt', '>'), ('le', '<='), ('ge', '>='),
        ('eq', ' == '), ('ne', '!=')
    ]:
        exec("def __%s__(self, ob): return self.__subject__ %s ob" % (name, op))

    for name, op in [('neg', '-'), ('pos', '+'), ('invert', '~')]:
        exec("def __%s__(self): return %s self.__subject__" % (name, op))

    for name, op in [
        ('or', '|'),  ('and', '&'), ('xor', '^'), ('lshift', '<<'), ('rshift', '>>'),
        ('add', '+'), ('sub', '-'), ('mul', '*'), ('div', '/'), ('mod', '%'),
        ('truediv', '/'), ('floordiv', '//')
    ]:
        exec((
            "def __%(name)s__(self, ob):\n"
            "    return self.__subject__ %(op)s ob\n"
            "\n"
            "def __r%(name)s__(self, ob):\n"
            "    return ob %(op)s self.__subject__\n"
            "\n"
            "def __i%(name)s__(self, ob):\n"
            "    self.__subject__ %(op)s=ob\n"
            "    return self\n"
        ) % locals())

    del name, op

    # Oddball signatures
    def __index__(self):
        return self.__subject__.__index__()

    def __rdivmod__(self, ob):
        return divmod(ob, self.__subject__)

    def __pow__(self, *args):
        return pow(self.__subject__, *args)

    def __ipow__(self, ob):
        self.__subject__ **= ob
        return self

    def __rpow__(self, ob):
        return pow(ob, self.__subject__)


class ObjectProxy(AbstractProxy):
    """Proxy for a specific object"""

    __slots__ = "__subject__"

    def __init__(self, subject):
        self.__subject__ = subject


class CallbackProxy(AbstractProxy):
    """Proxy for a dynamically-chosen object"""

    __slots__ = '__callback__'

    def __init__(self, func):
        set_callback(self, func)

set_callback = CallbackProxy.__callback__.__set__
get_callback = CallbackProxy.__callback__.__get__
CallbackProxy.__subject__ = property(lambda self, gc=get_callback: gc(self)())


class LazyProxy(CallbackProxy):
    """Proxy for a lazily-obtained object, that is cached on first use"""
    __slots__ = "__cache__"

get_cache = LazyProxy.__cache__.__get__
set_cache = LazyProxy.__cache__.__set__


def __subject__(self, get_cache=get_cache, set_cache=set_cache):
    try:
        return get_cache(self)
    except AttributeError:
        set_cache(self, get_callback(self)())
        return get_cache(self)

LazyProxy.__subject__ = property(__subject__, set_cache)
del __subject__


class AbstractWrapper(AbstractProxy):
    """Mixin to allow extra behaviors and attributes on proxy instance"""
    __slots__ = ()

    def __getattribute__(self, attr, oga=object.__getattribute__):
        if attr.startswith('__'):
            subject = oga(self, '__subject__')
            if attr == '__subject__':
                return subject
            return getattr(subject, attr)
        return oga(self, attr)

    def __getattr__(self, attr, oga=object.__getattribute__):
        return getattr(oga(self, '__subject__'), attr)

    def __setattr__(self, attr, val, osa=object.__setattr__):
        if (
            attr == '__subject__' or
            hasattr(type(self), attr) and not attr.startswith('__')
        ):
            osa(self, attr, val)
        else:
            setattr(self.__subject__, attr, val)

    def __delattr__(self, attr, oda=object.__delattr__):
        if (
            attr == '__subject__' or
            hasattr(type(self), attr) and not attr.startswith('__')
        ):
            oda(self, attr)
        else:
            delattr(self.__subject__, attr)


class ObjectWrapper(ObjectProxy, AbstractWrapper):
    __slots__ = ()


class CallbackWrapper(CallbackProxy, AbstractWrapper):
    __slots__ = ()


class LazyWrapper(LazyProxy, AbstractWrapper):
    __slots__ = ()


def lazymethod(method):
    """
    Decorator for overriding methods on LazyWrapper classes, that fill in until
    lazy initialization.
    """
    import functools

    @functools.wraps(method)
    def wrapper(self, *args, **kwargs):
        try:
            get_cache(self)
        except AttributeError:
            return method(self, *args, **kwargs)
        else:
            if method.__name__.startswith('__'):
                return getattr(LazyProxy, method.__name__)(self, *args, **kwargs)
            else:
                return getattr(self.__subject__, method.__name__)(*args, **kwargs)
    return wrapper