How to use the pymoca.ast.Slice function in pymoca

if free_var.is_symbolic():
                    if (len(self.for_loops) > 0) and (free_var.name() == self.for_loops[-1].name):
                        vals.append(self.for_loops[-1].index_variable)
                    else:
                        vals.append(self.get_integer(self.current_class.symbols[free_var.name()].value))

            # Evaluate the expression
            F = ca.Function('get_integer', free_vars, [expr])
            ret = F.call(vals, *self.function_mode)
            if ret[0].is_constant():
                # We managed to evaluate the expression.  Assume the result to be integer.
                return int(ret[0])
            else:
                # Expression depends on other symbols.  Could not extract integer value.
                return ret[0]
        if isinstance(tree, ast.Slice):
            start = self.get_integer(tree.start)
            step = self.get_integer(tree.step)
            stop = self.get_integer(tree.stop)
            return slice(start, stop, step)
        else:
            raise Exception('Unexpected node type {}'.format(tree.__class__.__name__))