def install(self, backend='money.exchange.SimpleBackend'):
        """Install an exchange rates backend using a python path string"""
        # RADAR: Python2
        if isinstance(backend, money.six.string_types):
            path, name = backend.rsplit('.', 1)
            module = importlib.import_module(path)
            backend = getattr(module, name)()
        elif isinstance(backend, type):
            backend = backend()
        if not isinstance(backend, BackendBase):
            raise TypeError("backend '{}' is not a subclass of "
                            "money.xrates.BackendBase".format(backend))
        self._backend = backend