Модель Keras 'fit_generator()
предполагает генератор, который создает кортежи формы (вход, цели), где оба элемента являются массивами NumPy. Документация, похоже, подразумевает, что если я просто завершу Dataset
iterator в генераторе, и обязательно преобразуйте массивы Tensors в NumPy, я должен хорошо идти. Этот код, однако, дает мне ошибку:
import numpy as np
import os
import keras.backend as K
from keras.layers import Dense, Input
from keras.models import Model
import tensorflow as tf
from tensorflow.contrib.data import Dataset
os.environ['TF_CPP_MIN_LOG_LEVEL'] = '3'
with tf.Session() as sess:
def create_data_generator():
dat1 = np.arange(4).reshape(-1, 1)
ds1 = Dataset.from_tensor_slices(dat1).repeat()
dat2 = np.arange(5, 9).reshape(-1, 1)
ds2 = Dataset.from_tensor_slices(dat2).repeat()
ds = Dataset.zip((ds1, ds2)).batch(4)
iterator = ds.make_one_shot_iterator()
while True:
next_val = iterator.get_next()
yield sess.run(next_val)
datagen = create_data_generator()
input_vals = Input(shape=(1,))
output = Dense(1, activation='relu')(input_vals)
model = Model(inputs=input_vals, outputs=output)
model.compile('rmsprop', 'mean_squared_error')
model.fit_generator(datagen, steps_per_epoch=1, epochs=5,
verbose=2, max_queue_size=2)
Вот ошибка, которую я получаю:
Using TensorFlow backend.
Epoch 1/5
Exception in thread Thread-1:
Traceback (most recent call last):
File "/home/jsaporta/anaconda3/lib/python3.6/site-packages/tensorflow/python/client/session.py", line 270, in __init__
fetch, allow_tensor=True, allow_operation=True))
File "/home/jsaporta/anaconda3/lib/python3.6/site-packages/tensorflow/python/framework/ops.py", line 2708, in as_graph_element
return self._as_graph_element_locked(obj, allow_tensor, allow_operation)
File "/home/jsaporta/anaconda3/lib/python3.6/site-packages/tensorflow/python/framework/ops.py", line 2787, in _as_graph_element_locked
raise ValueError("Tensor %s is not an element of this graph." % obj)
ValueError: Tensor Tensor("IteratorGetNext:0", shape=(?, 1), dtype=int64) is not an element of this graph.
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "/home/jsaporta/anaconda3/lib/python3.6/threading.py", line 916, in _bootstrap_inner
self.run()
File "/home/jsaporta/anaconda3/lib/python3.6/threading.py", line 864, in run
self._target(*self._args, **self._kwargs)
File "/home/jsaporta/anaconda3/lib/python3.6/site-packages/keras/utils/data_utils.py", line 568, in data_generator_task
generator_output = next(self._generator)
File "./datagen_test.py", line 25, in create_data_generator
yield sess.run(next_val)
File "/home/jsaporta/anaconda3/lib/python3.6/site-packages/tensorflow/python/client/session.py", line 895, in run
run_metadata_ptr)
File "/home/jsaporta/anaconda3/lib/python3.6/site-packages/tensorflow/python/client/session.py", line 1109, in _run
self._graph, fetches, feed_dict_tensor, feed_handles=feed_handles)
File "/home/jsaporta/anaconda3/lib/python3.6/site-packages/tensorflow/python/client/session.py", line 413, in __init__
self._fetch_mapper = _FetchMapper.for_fetch(fetches)
File "/home/jsaporta/anaconda3/lib/python3.6/site-packages/tensorflow/python/client/session.py", line 233, in for_fetch
return _ListFetchMapper(fetch)
File "/home/jsaporta/anaconda3/lib/python3.6/site-packages/tensorflow/python/client/session.py", line 340, in __init__
self._mappers = [_FetchMapper.for_fetch(fetch) for fetch in fetches]
File "/home/jsaporta/anaconda3/lib/python3.6/site-packages/tensorflow/python/client/session.py", line 340, in <listcomp>
self._mappers = [_FetchMapper.for_fetch(fetch) for fetch in fetches]
File "/home/jsaporta/anaconda3/lib/python3.6/site-packages/tensorflow/python/client/session.py", line 241, in for_fetch
return _ElementFetchMapper(fetches, contraction_fn)
File "/home/jsaporta/anaconda3/lib/python3.6/site-packages/tensorflow/python/client/session.py", line 277, in __init__
'Tensor. (%s)' % (fetch, str(e)))
ValueError: Fetch argument <tf.Tensor 'IteratorGetNext:0' shape=(?, 1) dtype=int64> cannot be interpreted as a Tensor. (Tensor Tensor("IteratorGetNext:0", shape=(?, 1), dtype=int64) is not an element of this graph.)
Traceback (most recent call last):
File "./datagen_test.py", line 34, in <module>
verbose=2, max_queue_size=2)
File "/home/jsaporta/anaconda3/lib/python3.6/site-packages/keras/legacy/interfaces.py", line 87, in wrapper
return func(*args, **kwargs)
File "/home/jsaporta/anaconda3/lib/python3.6/site-packages/keras/engine/training.py", line 2011, in fit_generator
generator_output = next(output_generator)
StopIteration
Как ни странно, добавление строки, содержащей next(datagen)
непосредственно после того, где я инициализирую datagen
, заставляет код работать нормально, без ошибок.
Почему мой исходный код не работает? Почему он начинает работать, когда я добавляю эту строку в свой код? Есть ли более эффективный способ использования TensorFlow Dataset API с Keras, который не включает преобразование тензоров в массивы NumPy и обратно?