停止迭代:generator_output = next(output_generator) [英] StopIteration: generator_output = next(output_generator)

问题描述

我有以下代码，我重写了这些代码以处理大规模数据集.我正在使用 Python 生成器在逐批生成的数据上拟合模型.

I have the following code which I rewrite to work on a large scale dataset. I am using Python generator to Fit the model on data yielded batch-by-batch.

def subtract_mean_gen(x_source,y_source,avg_image,batch):
    batch_list_x=[]
    batch_list_y=[]
    for line,y in zip(x_source,y_source):
        x=line.astype('float32')
        x=x-avg_image
        batch_list_x.append(x)
        batch_list_y.append(y)
        if len(batch_list_x) == batch:
            yield (np.array(batch_list_x),np.array(batch_list_y))
            batch_list_x=[]
            batch_list_y=[] 

model = resnet.ResnetBuilder.build_resnet_18((img_channels, img_rows, img_cols), nb_classes)
model.compile(loss='categorical_crossentropy',
              optimizer='adam',
              metrics=['accuracy'])

val = subtract_mean_gen(X_test,Y_test,avg_image_test,batch_size)
model.fit_generator(subtract_mean_gen(X_train,Y_train,avg_image_train,batch_size), steps_per_epoch=X_train.shape[0]//batch_size,epochs=nb_epoch,validation_data = val,
                    validation_steps = X_test.shape[0]//batch_size)

我收到以下错误:

239/249 [===========================>..] - ETA: 60s - loss: 1.3318 - acc: 0.8330Exception in thread Thread-1:
Traceback (most recent call last):
  File "/usr/lib/python2.7/threading.py", line 801, in __bootstrap_inner
    self.run()
  File "/usr/lib/python2.7/threading.py", line 754, in run
    self.__target(*self.__args, **self.__kwargs)
  File "/usr/local/lib/python2.7/dist-packages/keras/utils/data_utils.py", line 560, in data_generator_task
    generator_output = next(self._generator)
StopIteration

240/249 [===========================>..] - ETA: 54s - loss: 1.3283 - acc: 0.8337Traceback (most recent call last):
  File "cifa10-copy.py", line 125, in <module>
    validation_steps = X_test.shape[0]//batch_size)
  File "/usr/local/lib/python2.7/dist-packages/keras/legacy/interfaces.py", line 87, in wrapper
    return func(*args, **kwargs)
  File "/usr/local/lib/python2.7/dist-packages/keras/engine/training.py", line 1809, in fit_generator
    generator_output = next(output_generator)
StopIteration

我调查了在此处发布的类似问题 但是，我无法解决引发 StopIteration 的错误.

I looked into a similar question posted here however, I am not able to resolve the error why StopIteration is raised.

推荐答案

keras 的生成器必须是无限的:

Generators for keras must be infinite:

def subtract_mean_gen(x_source,y_source,avg_image,batch):
    while True:
        batch_list_x=[]
        batch_list_y=[]
        for line,y in zip(x_source,y_source):
            x=line.astype('float32')
            x=x-avg_image
            batch_list_x.append(x)
            batch_list_y.append(y)
            if len(batch_list_x) == batch:
                yield (np.array(batch_list_x),np.array(batch_list_y))
                batch_list_x=[]
                batch_list_y=[] 

发生错误是因为 keras 尝试获取新批次，但您的生成器已经到达终点.(即使您定义了正确的步骤数，keras 也有一个队列，即使您处于最后一步，它也会尝试从生成器中获取更多批次.)

The error happens because keras tries to get a new batch, but your generator has already reached its end. (Even though you defined a correct number of steps, keras has a queue that will be trying to get more batches from the generator even if you are at the last step.)

显然，您有一个默认的队列大小，即 10(在结束前 10 个批次出现异常，因为队列试图在结束后获取批次).

Apparently, you've got a default queue size, which is 10 (the exception appears 10 batches before the end because the queue is trying to get a batch after the end).

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