什么引起了我的Keras Model.fit_generator中的StopIteration

Question

我有下一个代码:

from sklearn.model_selection import train_test_split
from scipy.misc import imresize

def _chunks(l, n):
    """Yield successive n-sized chunks from l."""
    for i in range(0, len(l), n):
        yield l[i:i + n]


def _batch_generator(data, batch_size):
    indexes = range(len(data))
    index_chunks = _chunks(indexes, batch_size)
    for i, indexes in enumerate(index_chunks):
        print("\nLoaded batch {0}\n".format(i + 1))
        batch_X = []
        batch_y = []
        for index in indexes:
            record = data[index]
            image = _read_train_image(record["id"], record["index"])
            mask = _read_train_mask(record["id"], record["index"])
            mask_resized = imresize(mask, (1276, 1916)) >= 123
            mask_reshaped = mask_resized.reshape((1276, 1916, 1))
            batch_X.append(image)
            batch_y.append(mask_reshaped)
        np_batch_X = np.array(batch_X)
        np_batch_y = np.array(batch_y)
        yield np_batch_X, np_batch_y


def train(data, model, batch_size, epochs):
    train_data, test_data = train_test_split(data)
    samples_per_epoch = len(train_data)
    steps_per_epoch = samples_per_epoch // batch_size
    print("Train on {0} records ({1} batches)".format(samples_per_epoch, steps_per_epoch))
    train_generator = _batch_generator(train_data, batch_size)
    model.fit_generator(train_generator, 
                        steps_per_epoch=steps_per_epoch, 
                        nb_epoch=epochs, 
                        verbose=1)

train(train_indexes[:30], autoencoder,
    batch_size=2,
    epochs=1)

所以看起来它必须在下一步工作:

• 从数据集中获取30个(仅示例)索引
• 吐出22条火车记录和8条验证指标(尚未使用)
• 将火车索引拆分为生成器中的2个索引批次(所以 - 11个批次)并且它的工作原理 - len(list(_batch_generator(train_indexes[:22], 2)))真正返回11
• 合身模特:
  • 在train_generator生成的批次上(在我的案例中 - 11批,每个 - 2张图片)
  • 11个批次在epoch(steps_per_epoch=steps_per_epoch)
  • 和1个纪元(nb_epochs=epochs,epochs=1)

但输出有下一个观点:

Train on 22 records (11 batches)
Epoch 1/1

Loaded batch 1

C:\Users\user\venv\machinelearning\lib\site-packages\ipykernel_launcher.py:39: UserWarning: The semantics of the Keras 2 argument `steps_per_epoch` is not the same as the Keras 1 argument `samples_per_epoch`. `steps_per_epoch` is the number of batches to draw from the generator at each epoch. Basically steps_per_epoch = samples_per_epoch/batch_size. Similarly `nb_val_samples`->`validation_steps` and `val_samples`->`steps` arguments have changed. Update your method calls accordingly.
C:\Users\user\venv\machinelearning\lib\site-packages\ipykernel_launcher.py:39: UserWarning: Update your `fit_generator` call to the Keras 2 API: `fit_generator(<generator..., steps_per_epoch=11, verbose=1, epochs=1)`

Loaded batch 2

1/11 [=>............................] - ETA: 11s - loss: 0.7471
Loaded batch 3


Loaded batch 4


Loaded batch 5


Loaded batch 6

2/11 [====>.........................] - ETA: 17s - loss: 0.7116
Loaded batch 7


Loaded batch 8


Loaded batch 9


Loaded batch 10

3/11 [=======>......................] - ETA: 18s - loss: 0.6931
Loaded batch 11

Exception in thread Thread-50:
Traceback (most recent call last):
File "C:\Anaconda3\Lib\threading.py", line 916, in _bootstrap_inner
    self.run()
File "C:\Anaconda3\Lib\threading.py", line 864, in run
    self._target(*self._args, **self._kwargs)
File "C:\Users\user\venv\machinelearning\lib\site-packages\keras\utils\data_utils.py", line 560, in data_generator_task
    generator_output = next(self._generator)
StopIteration

4/11 [=========>....................] - ETA: 18s - loss: 0.6663
---------------------------------------------------------------------------
StopIteration                             Traceback (most recent call last)
<ipython-input-16-092ba6eb51d2> in <module>()
    1 train(train_indexes[:30], autoencoder,
    2       batch_size=2,
----> 3       epochs=1)

<ipython-input-15-f2fec4e53382> in train(data, model, batch_size, epochs)
    37                         steps_per_epoch=steps_per_epoch,
    38                         nb_epoch=epochs,
---> 39                         verbose=1)

C:\Users\user\venv\machinelearning\lib\site-packages\keras\legacy\interfaces.py in wrapper(*args, **kwargs)
    85                 warnings.warn('Update your `' + object_name +
    86                               '` call to the Keras 2 API: ' + signature, stacklevel=2)
---> 87             return func(*args, **kwargs)
    88         wrapper._original_function = func
    89         return wrapper

C:\Users\user\venv\machinelearning\lib\site-packages\keras\engine\training.py in fit_generator(self, generator, steps_per_epoch, epochs, verbose, callbacks, validation_data, validation_steps, class_weight, max_queue_size, workers, use_multiprocessing, initial_epoch)
1807                 batch_index = 0
1808                 while steps_done < steps_per_epoch:
-> 1809                     generator_output = next(output_generator)
1810 
1811                     if not hasattr(generator_output, '__len__'):

StopIteration: 

所以我可以看到 - 所有批次都是成功的(参见"已加载的批次")

但是在处理第1纪元的第3批时,keras引发了StopIteration.

Answer 1

我也遇到了这个问题，我发现一种方法是可以在数据生成器函数中插入“ while True”块。但我无法获得消息来源。您可以参考以下代码：

while True:
     assert len(inputs) == len(targets)
     indices = np.arange(len(inputs))
     if shuffle:
        np.random.shuffle(indices)
     if batchsize > len(indices):
        sys.stderr.write('BatchSize out of index size')
     batchsize = len(indices)
     for start_idx in range(0, len(inputs) - batchsize + 1, batchsize):
         if shuffle:
            excerpt = indices[start_idx:start_idx + batchsize]
         else:
            excerpt = slice(start_idx, start_idx + batchsize)
         yield inputs[excerpt], targets[excerpt]

Answer 2

我找到了问题根源。首先 - 我的数据集在拟合结束之前已完全读取，因此它会引发

Exception in thread Thread-50:
Traceback (most recent call last):
File "C:\Anaconda3\Lib\threading.py", line 916, in _bootstrap_inner
self.run()
File "C:\Anaconda3\Lib\threading.py", line 864, in run
self._target(*self._args, **self._kwargs)
File "C:\Users\user\venv\machinelearning\lib\site-packages\keras\utils\data_utils.py", line 560, in data_generator_task
generator_output = next(self._generator)
StopIteration

异常处理程序设置 stop_event 并重新引发异常

但 ：

def get(self):
    """Creates a generator to extract data from the queue.

    Skip the data if it is `None`.

    # Returns
        A generator
    """
    while self.is_running():
        if not self.queue.empty():
            inputs = self.queue.get()
            if inputs is not None:
                yield inputs
        else:
            time.sleep(self.wait_time)

因此，当设置停止事件时 - 它可以从队列加载数据

所以我将 max_queue_size 限制为 1。