Created by: lgone2000

如下面测试程序所示， default_startup_program 调用顺序不对，而报的错误比较乱，估计这种错误困扰了很多人， 希望paddle能改一下。

def test_error_report():
    place = fluid.CPUPlace()
    exe = fluid.Executor(place)
    main_program = fluid.default_main_program()
    x = fluid.layers.data(name='x', shape=[10], dtype='float32')
    feature = fluid.layers.fc(name='fc', input=x, size=20, act=None)
    loss = fluid.layers.reduce_mean(feature)
    
    if 1:
        #这个代码报错信息完全看不懂， 能否简单报一个，default_startup_program 应在minimize后执行？
        exe.run(fluid.default_startup_program())
        optimizer = fluid.optimizer.SGD(learning_rate=0.1)
        opts = optimizer.minimize(loss)
    else:
        optimizer = fluid.optimizer.SGD(learning_rate=0.1)
        opts = optimizer.minimize(loss)
        exe.run(fluid.default_startup_program())
        
    batch_data = np.random.rand(5,10).astype(np.float32)
    output = exe.run(main_program,feed={'x': batch_data},fetch_list=[loss])