def change_attr_expression(thread_id, frame_id, attr, expression, dbg, value=SENTINEL_VALUE):
    '''Changes some attribute in a given frame.
    '''
    frame = find_frame(thread_id, frame_id)
    if frame is None:
        return

    try:
        expression = expression.replace('@LINE@', '\n')

        if dbg.plugin and value is SENTINEL_VALUE:
            result = dbg.plugin.change_variable(frame, attr, expression)
            if result:
                return result

        if attr[:7] == "Globals":
            attr = attr[8:]
            if attr in frame.f_globals:
                if value is SENTINEL_VALUE:
                    value = eval(expression, frame.f_globals, frame.f_locals)
                frame.f_globals[attr] = value
                return frame.f_globals[attr]
        else:
            if '.' not in attr:  # i.e.: if we have a '.', we're changing some attribute of a local var.
                if pydevd_save_locals.is_save_locals_available():
                    if value is SENTINEL_VALUE:
                        value = eval(expression, frame.f_globals, frame.f_locals)
                    frame.f_locals[attr] = value
                    pydevd_save_locals.save_locals(frame)
                    return frame.f_locals[attr]

            # default way (only works for changing it in the topmost frame)
            if value is SENTINEL_VALUE:
                value = eval(expression, frame.f_globals, frame.f_locals)
            result = value
            Exec('%s=%s' % (attr, expression), frame.f_globals, frame.f_locals)
            return result


    except Exception:
        traceback.print_exc()
Changes some attribute in a given frame.
    
debugger/src/_pydevd_bundle/pydevd_vars.py