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# Copyright 2017 The TensorFlow Authors. All Rights Reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
# ==============================================================================
"""Python wrappers for Iterators."""
from __future__ import absolute_import
from __future__ import division
from __future__ import print_function
from tensorflow.python.data.util import nest
from tensorflow.python.framework import dtypes
from tensorflow.python.framework import ops
from tensorflow.python.framework import tensor_shape
from tensorflow.python.ops import gen_dataset_ops
class Iterator(object):
"""Represents the state of iterating through a `Dataset`."""
def __init__(self, iterator_resource, initializer, output_types,
output_shapes):
"""Creates a new iterator from the given iterator resource.
Note: Most users will not call this initializer directly, and will
instead use `Dataset.make_initializable_iterator()` or
`Dataset.make_one_shot_iterator()`.
Args:
iterator_resource: A `tf.resource` scalar `tf.Tensor` representing the
iterator.
initializer: A `tf.Operation` that should be run to initialize this
iterator.
output_types: A nested structure of `tf.DType` objects corresponding to
each component of an element of this iterator.
output_shapes: A nested structure of `tf.TensorShape` objects
corresponding to each component of an element of this dataset.
"""
self._iterator_resource = iterator_resource
self._initializer = initializer
self._output_types = output_types
self._output_shapes = output_shapes
@staticmethod
def from_structure(output_types, output_shapes=None, shared_name=None):
"""Creates a new, uninitialized `Iterator` with the given structure.
This iterator-constructing method can be used to create an iterator that
is reusable with many different datasets.
The returned iterator is not bound to a particular dataset, and it has
no `initializer`. To initialize the iterator, run the operation returned by
`Iterator.make_initializer(dataset)`.
The following is an example
```python
iterator = Iterator.from_structure(tf.int64, tf.TensorShape([]))
dataset_range = Dataset.range(10)
range_initializer = iterator.make_initializer(dataset_range)
dataset_evens = dataset_range.filter(lambda x: x % 2 == 0)
evens_initializer = iterator.make_initializer(dataset_evens)
# Define a model based on the iterator; in this example, the model_fn
# is expected to take scalar tf.int64 Tensors as input (see
# the definition of 'iterator' above).
prediction, loss = model_fn(iterator.get_next())
# Train for `num_epochs`, where for each epoch, we first iterate over
# dataset_range, and then iterate over dataset_evens.
for _ in range(num_epochs):
# Initialize the iterator to `dataset_range`
sess.run(range_initializer)
while True:
try:
pred, loss_val = sess.run([prediction, loss])
except tf.errors.OutOfRangeError:
break
# Initialize the iterator to `dataset_evens`
sess.run(evens_initializer)
while True:
try:
pred, loss_val = sess.run([prediction, loss])
except tf.errors.OutOfRangeError:
break
```
Args:
output_types: A nested structure of `tf.DType` objects corresponding to
each component of an element of this iterator.
output_shapes: (Optional.) A nested structure of `tf.TensorShape` objects
corresponding to each component of an element of this dataset. If
omitted, each component will have an unconstrainted shape.
shared_name: (Optional.) If non-empty, this iterator will be shared under
the given name across multiple sessions that share the same devices
(e.g. when using a remote server).
Returns:
An `Iterator`.
Raises:
TypeError: If the structures of `output_shapes` and `output_types` are
not the same.
"""
output_types = nest.map_structure(dtypes.as_dtype, output_types)
if output_shapes is None:
output_shapes = nest.map_structure(
lambda _: tensor_shape.TensorShape(None), output_types)
else:
output_shapes = nest.map_structure_up_to(
output_types, tensor_shape.as_shape, output_shapes)
nest.assert_same_structure(output_types, output_shapes)
if shared_name is None:
shared_name = ""
iterator_resource = gen_dataset_ops.iterator(
container="",
shared_name=shared_name,
output_types=nest.flatten(output_types),
output_shapes=nest.flatten(output_shapes))
return Iterator(iterator_resource, None, output_types, output_shapes)
@staticmethod
def from_string_handle(string_handle, output_types, output_shapes=None):
"""Creates a new, uninitialized `Iterator` based on the given handle.
This method allows you to define a "feedable" iterator where you can choose
between concrete iterators by feeding a value in a @{tf.Session.run} call.
In that case, `string_handle` would a @{tf.placeholder}, and you would feed
it with the value of @{tf.contrib.data.Iterator.string_handle} in each step.
For example, if you had two iterators that marked the current position in
a training dataset and a test dataset, you could choose which to use in
each step as follows:
```python
train_iterator = tf.contrib.data.Dataset(...).make_one_shot_iterator()
train_iterator_handle = sess.run(train_iterator.string_handle())
test_iterator = tf.contrib.data.Dataset(...).make_one_shot_iterator()
test_iterator_handle = sess.run(test_iterator.string_handle())
handle = tf.placeholder(tf.string, shape=[])
iterator = tf.contrib.data.Iterator.from_string_handle(
handle, train_iterator.output_types)
next_element = iterator.get_next()
loss = f(next_element)
train_loss = sess.run(loss, feed_dict={handle: train_iterator_handle})
test_loss = sess.run(loss, feed_dict={handle: test_iterator_handle})
```
Args:
string_handle: A scalar `tf.Tensor` of type `tf.string` that evaluates
to a handle produced by the `Iterator.string_handle()` method.
output_types: A nested structure of `tf.DType` objects corresponding to
each component of an element of this iterator.
output_shapes: (Optional.) A nested structure of `tf.TensorShape` objects
corresponding to each component of an element of this dataset. If
omitted, each component will have an unconstrainted shape.
Returns:
An `Iterator`.
"""
output_types = nest.map_structure(dtypes.as_dtype, output_types)
if output_shapes is None:
output_shapes = nest.map_structure(
lambda _: tensor_shape.TensorShape(None), output_types)
else:
output_shapes = nest.map_structure_up_to(
output_types, tensor_shape.as_shape, output_shapes)
nest.assert_same_structure(output_types, output_shapes)
string_handle = ops.convert_to_tensor(string_handle, dtype=dtypes.string)
iterator_resource = gen_dataset_ops.iterator_from_string_handle(
string_handle,
output_types=nest.flatten(output_types),
output_shapes=nest.flatten(output_shapes))
return Iterator(iterator_resource, None, output_types, output_shapes)
@property
def initializer(self):
"""A `tf.Operation` that should be run to initialize this iterator.
Returns:
A `tf.Operation` that should be run to initialize this iterator
Raises:
ValueError: If this iterator initializes itself automatically.
"""
if self._initializer is not None:
return self._initializer
else:
# TODO(mrry): Consider whether one-shot iterators should have
# initializers that simply reset their state to the beginning.
raise ValueError("Iterator does not have an initializer.")
def make_initializer(self, dataset, name=None):
"""Returns a `tf.Operation` that initializes this iterator on `dataset`.
Args:
dataset: A `Dataset` with compatible structure to this iterator.
name: (Optional.) A name for the created operation.
Returns:
A `tf.Operation` that can be run to initialize this iterator on the given
`dataset`.
Raises:
TypeError: If `dataset` and this iterator do not have a compatible
element structure.
"""
with ops.name_scope(name, "make_initializer") as name:
nest.assert_same_structure(self._output_types, dataset.output_types)
nest.assert_same_structure(self._output_shapes, dataset.output_shapes)
for iterator_dtype, dataset_dtype in zip(
nest.flatten(self._output_types), nest.flatten(dataset.output_types)):
if iterator_dtype != dataset_dtype:
raise TypeError(
"Expected output types %r but got dataset with output types %r." %
(self._output_types, dataset.output_types))
for iterator_shape, dataset_shape in zip(
nest.flatten(self._output_shapes),
nest.flatten(dataset.output_shapes)):
if not iterator_shape.is_compatible_with(dataset_shape):
raise TypeError("Expected output shapes compatible with %r but got "
"dataset with output shapes %r." %
(self._output_shapes, dataset.output_shapes))
with ops.colocate_with(self._iterator_resource):
return gen_dataset_ops.make_iterator(
dataset._as_variant_tensor(), self._iterator_resource, name=name) # pylint: disable=protected-access
def get_next(self, name=None):
"""Returns a nested structure of `tf.Tensor`s containing the next element.
Args:
name: (Optional.) A name for the created operation.
Returns:
A nested structure of `tf.Tensor` objects.
"""
return nest.pack_sequence_as(
self._output_types,
gen_dataset_ops.iterator_get_next(
self._iterator_resource,
output_types=nest.flatten(self._output_types),
output_shapes=nest.flatten(self._output_shapes),
name=name))
def string_handle(self, name=None):
"""Returns a string-valued `tf.Tensor` that represents this iterator.
Args:
name: (Optional.) A name for the created operation.
Returns:
A scalar `tf.Tensor` of type `tf.string`.
"""
return gen_dataset_ops.iterator_to_string_handle(
self._iterator_resource, name=name)
@property
def output_shapes(self):
"""Returns the shape of each component of an element of this iterator.
Returns:
A nested structure of `tf.TensorShape` objects corresponding to each
component of an element of this iterator.
"""
return self._output_shapes
@property
def output_types(self):
"""Returns the type of each component of an element of this iterator.
Returns:
A nested structure of `tf.DType` objects corresponding to each component
of an element of this iterator.
"""
return self._output_types