def _get_vars(self, stack, scopes):
        """Get specifically scoped variables from a list of stack frames.

        Parameters
        ----------
        stack : list
            A list of stack frames as returned by ``inspect.stack()``
        scopes : sequence of strings
            A sequence containing valid stack frame attribute names that
            evaluate to a dictionary. For example, ('locals', 'globals')
        """
        variables = itertools.product(scopes, stack)
        for scope, (frame, _, _, _, _, _) in variables:
            try:
                d = getattr(frame, 'f_' + scope)
                self.scope = self.scope.new_child(d)
            finally:
                # won't remove it, but DECREF it
                # in Py3 this probably isn't necessary since frame won't be
                # scope after the loop
                del frame
Get specifically scoped variables from a list of stack frames.

        Parameters
        ----------
        stack : list
            A list of stack frames as returned by ``inspect.stack()``
        scopes : sequence of strings
            A sequence containing valid stack frame attribute names that
            evaluate to a dictionary. For example, ('locals', 'globals')