Created by: daming-lu

We found a bug while testing the new API. If we pass in trainer.train() a feed order of a list like below:

    trainer.train(
        reader=train_reader,
        num_epochs=100,
        event_handler=event_handler,
        feed_order=['x', 'y'])

Then later call the trainer.test() without a feed_order. Then the pre-defined order (in this case, ['x', 'y']) will not be respected. In trainer.test(), it would become ['y', 'x'].

The cause is here:

paddle/fluid/trainer.py(279)build_feed_var_list()

    if feed_order is None:
        feed_var_list = [
            var for var in program.global_block().vars.itervalues()
            if var.is_data
        ]

Inside program.global_block().vars.itervalues(), we converted the passed-in list into a dictionary thus the order is not obeyed.