def expression(self, string):
        """
        Interpret an expression string.  This returns a callable taking
        one argument--this context--and returning the result of
        evaluating the expression.

        :param string: The expression.

        :returns: A callable of one argument that will return the
                  desired expression.
        """

        # Short-circuit if the expression "string" isn't actually a
        # string
        if not isinstance(string, six.string_types):
            return lambda ctxt: string

        # Create the expression and return the callable
        expr = self._jinja.compile_expression(string)
        return lambda ctxt: expr(ctxt.variables)
Interpret an expression string.  This returns a callable taking
        one argument--this context--and returning the result of
        evaluating the expression.

        :param string: The expression.

        :returns: A callable of one argument that will return the
                  desired expression.