transparent object restarts

restartable.py

class Restartable(object):
    @classmethod
    def __new__(cls, *args, **kwargs):
        ret = super(Restartable, cls).__new__(*args, **kwargs)
        ret.__initargs__ = (args[1:], kwargs)
        return ret

    # this is something like a clone with __getinitargs__ but let's not call
    # it a clone because it's semantically different--i.e. explicitly discards
    # any state other than the initial one.
    def restart(self):
        print "restarting %s with %s" % (self, self.__initargs__)
        init_args, init_kwargs = self.__initargs__
        return type(self)(*init_args, **init_kwargs)


class Foo(Restartable):
    def __init__(self, a, b):
        print "Foo(a=%s, b=%s)" % (repr(a), repr(b))


class Bar(Foo):
    def __init__(self, extra, *args, **kwargs):
        super(Bar, self).__init__(*args, **kwargs)
        print "Bar(extra=%s)" % repr(extra)


foo = Foo(1, 2)
foo = foo.restart()

bar = Bar('extra', 4, 5)
bar = bar.restart()