events.py 文件源码

def _listen(cls, target, identifier, fn, retval=False):
        target._has_events = True

        if not retval:
            if identifier == 'before_execute':
                orig_fn = fn

                def wrap_before_execute(conn, clauseelement,
                                                multiparams, params):
                    orig_fn(conn, clauseelement, multiparams, params)
                    return clauseelement, multiparams, params
                fn = wrap_before_execute
            elif identifier == 'before_cursor_execute':
                orig_fn = fn

                def wrap_before_cursor_execute(conn, cursor, statement,
                        parameters, context, executemany):
                    orig_fn(conn, cursor, statement,
                        parameters, context, executemany)
                    return statement, parameters
                fn = wrap_before_cursor_execute

        elif retval and \
            identifier not in ('before_execute', 'before_cursor_execute'):
            raise exc.ArgumentError(
                    "Only the 'before_execute' and "
                    "'before_cursor_execute' engine "
                    "event listeners accept the 'retval=True' "
                    "argument.")
        event.Events._listen(target, identifier, fn)