code: # Copyright (c) 2019 PaddlePaddle 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.
  
  from . import core
  import sys
  import six
  import numpy as np
  import threading
  import paddle
  from .framework import Program, Variable, program_guard, default_main_program, default_startup_program, in_dygraph_mode, cpu_places, _current_expected_place, _in_eager_mode
  from .executor import global_scope
  from .data_feeder import DataFeeder, BatchedTensorProvider
  from .multiprocess_utils import multiprocess_queue_set, CleanupFuncRegistrar, _cleanup_mmap, _cleanup, _set_SIGCHLD_handler
  from .dataloader import BatchSampler, Dataset, IterableDataset
  from .dataloader.dataloader_iter import _DataLoaderIterSingleProcess, _DataLoaderIterMultiProcess, _DatasetKind, default_collate_fn
  from .dataloader.batch_sampler import _InfiniteIterableSampler
  from .layers.io import monkey_patch_reader_methods, _copy_reader_var_, double_buffer
  from .unique_name import UniqueNameGenerator
  from .framework import _get_paddle_place, _get_paddle_place_list
  from paddle.fluid.framework import _set_expected_place, _current_expected_place
  import logging
  import warnings
  
  ### Dygraph DataLoader configs ###
  import os
  import multiprocessing
  import signal
  
  # NOTE: queue has a different name in python2 and python3
  import queue
  
  # NOTE: [ avoid hanging & failed quickly ] These value is used in getting data from another process
  QUEUE_GET_TIMEOUT = 60
  
  __all__ = ['PyReader', 'DataLoader', 'default_collate_fn']
  
  data_loader_unique_name_generator = UniqueNameGenerator()
  
  KEEP_DATA_LOADER_ORDER = True
  USE_PINNED_MEMORY = None
  
  
  def keep_data_loader_order(*args):
      global KEEP_DATA_LOADER_ORDER
      if len(args) == 0:
          return KEEP_DATA_LOADER_ORDER
      else:
          assert len(args) == 1 and isinstance(args[0], bool)
          KEEP_DATA_LOADER_ORDER = args[0]
  
  
  def use_pinned_memory(*args):
      global USE_PINNED_MEMORY
      if len(args) == 0:
          return USE_PINNED_MEMORY
      else:
          assert len(args) == 1 and isinstance(args[0], bool)
          USE_PINNED_MEMORY = args[0]
  
  
  def _convert_places(places):
      if not isinstance(places, (list, tuple)):
          places = [places]
  
      ret = []
      for p in places:
          if not isinstance(p, core.Place):
              tmp = core.Place()
              tmp.set_place(p)
              p = tmp
  
          ret.append(p)
      return ret
  
  
  # NOTE(chenweihang): _reader_process_loop must be top level method to be pickled
  def _reader_process_loop(batch_reader, data_queue):
      try:
          # set signal handler
          core._set_process_signal_handler()
  
          # NOTE: [ mmap files clear ] When the child process exits unexpectedly,
          # some shared memory objects may have been applied for but have not yet
          # been put into the inter-process Queue. This part of the object needs
          # to be cleaned up when the process ends.
          CleanupFuncRegistrar.register(_cleanup_mmap)
  
          for batch in batch_reader():
              tensor_list = core._convert_to_tensor_list(batch)
              data_queue.put(tensor_list)
              core._remove_tensor_list_mmap_fds(tensor_list)
          data_queue.put(None)
      except KeyboardInterrupt:
          # NOTE: Main process will raise KeyboardInterrupt anyways, ignore it in child process
          pass
      except:
          six.reraise(*sys.exc_info())
  
  
  class DataLoaderBase(object):
      def __init__(self):
          self._places = None
  
      def __call__(self):
          return self
  
      def next(self):
          '''
          Get the next item in the DataLoader object. This method    
          should not be called by users directly. It is used for
          implementing iterator protocol of Python 2.x inside
          PaddlePaddle framework.
          '''
          return self.__next__()
  
      def __iter__(self):
          raise NotImplementedError()
  
      def __next__(self):
          raise NotImplementedError()
  
      @classmethod
      def _check_input_array(cls, item):
          arr = np.asarray(item)
          if arr.dtype == np.object:
              raise TypeError(
                  "\n\tFaild to convert input data to a regular ndarray :\n\t* Usually "
                  "this means the input data contains nested lists with different lengths. "
                  "\n\t* Check the reader function passed to 'decorate_batch_generator'"
                  " to locate the data causes this issue.\n\t* Please consider using "
                  "'fluid.create_lod_tensor' to convert it to a LoD-Tensor.")
          return arr
  
  
  class DataLoader(object):
      """
      DataLoader prodives an iterator which iterates given dataset
      once by the batch_sampler.
  
      DataLoader supports single-process and multi-prcess data loading,
      multi-process workers will be used to load data asynchronously if
      :attr:`num_workers` is set as a positive number.
  
      DataLoader supports map-style dataset and iterable-style dataset.
  
      For map-style datast(can get a sample from dataset with a given
      index), please see :code:`paddle.io.Dataset`.
  
      For iterable-style datast(get samples from dataset iteratively,
      like a Python iterator), please see :code:`paddle.io.IterableDataset`.
  
      For :code:`batch_sampler` please see :code:`paddle.io.BatchSampler`
  
      .. note::
          GPU tensor operation is not supported in subprocess currently,
          please don't use GPU tensor operations in pipeline which will
          be performed in subprocess, such as dataset transforms, collte_fn,
          etc. Numpy array and CPU tensor operation is supported.
  
      **Disable automatic batching**
  
      In certain cases such as some NLP tasks, instead of automatic batching,
      handling batching manually in dataset is needed by users. For these
      cases, automatic batching is disabled if both :attr:`batch_size` and
      :attr:`batch_sampler` is set as None, each data got from :attr:`dataset`
      should be batched data and will be processed with function define by
      :attr:`collate_fn` or :attr:`default_collate_fn`.
  
  
      .. note::
          When automatic batching is disabled, :attr:`default_collate_fn` will
          do nothing to data from dataset.
  
  
      Args:  
          dataset(Dataset): the dataset to load data from, should be an
              instance of subclass of :code:`paddle.io.Dataset` or
              :code:`paddle.io.IterableDataset`.
          feed_list (list(Tensor)|tuple(Tensor)): feed Tensor list.
              The Tensors should be created by :code:`paddle.static.data()`.
              :attr:`feed_list` must be set if :attr:`return_list` is
              False. Default None.
          places(list(Place)|tuple(Place)|list(str)|optional): a list of Place,
              to put data onto, :attr:`places` can be None, if 
              :attr:`places` is None, default place(CPUPlace or CUDAPlace(0))
              will be used. Default None. If ``places`` is list of string,
              the string in the list can be ``cpu``, ``gpu:x`` and ``gpu_pinned``,
              where ``x`` is the index of the GPUs.
          return_list (bool): whether the return value on each device is 
              presented as a list. If :attr:`return_list=False`, the return
              value on each device would be a dict of str -> Tensor, where
              the key of the dict is the name of each fed Tensors. If 
              :attr:`return_list=True`, the return value on each device would
              be a list(Tensor). :attr:`return_list` can only be True
              in dynamic graph mode. Default True.
          batch_sampler(BatchSampler): an instance of `paddle.io.BatchSampler`
              to generate batch indices to draw samples from :attr:`dataset`
              and combine a batch. Default None.
          batch_size(int|None): sample number in a mini-batch, a substitution
              parameter for :attr:`batch_sampler`, if :attr:`batch_sampler`
              is not set, a default `paddle.io.BatchSampler` will be used
              and initialize by :attr:`batch_size`, :attr:`shuffle` and
              :attr:`drop_last`. Default 1.
          shuffle(bool): whther to shuffle indices order before genrate
              batch indices, a substitution parameter for :attr:`batch_sampler`
              see :attr:`batch_size`. Default False.
          drop_last(bool): whether drop the last incomplete batch dataset size
              is not divisible by the batch size, a substitution parameter
              for :attr:`batch_sampler`, see :attr:`batch_size`. Default False
          collate_fn(callable): function to generate mini-batch data by merging
              the sample list, None for only stack each fields of sample in axis
              0(same as :attr::`np.stack(..., axis=0)`). Default None
          num_workers(int): the number of subprocess to load data, 0 for no
              subprocess used and loading data in main process. Default 0
          use_buffer_reader (bool): whether to use bufferred reader. 
              If use_buffer_reader=True, the DataLoader would prefetch next 
              batch data asynchronously, so it would speed up data feeding 
              and occupies a little more CPU or GPU memory, i.e., the memory
              of one batch input data. Default True.
          use_shared_memory (bool): whether to use shared memory to speed up
              putting data into inter-process queue, set :attr:`use_shared_memory`
              as True only when the shared memory space on your machine(e.g.
              space of '/dev/shm' on Linux operating sysytem) is large enough.
              Shared memory will only be enabled in multi-process mode(num_workers
              > 0). Default True.
          timeout(int): the timeout value for getting data form output queue
              of subprocesses. Default 0.
          worker_init_fn(callable): init function which will be called with
              worker id on each subproces starting if not set as None. Default
              None.
  
      Returns:
          DataLoader: an iterable object for data iterating, each elemnet of the generated data is a Tensor.
  
      Examples:
          
          .. code-block:: python
  
              import numpy as np
  
              import paddle
              import paddle.nn as nn
              import paddle.nn.functional as F
              from paddle.io import Dataset, BatchSampler, DataLoader
  
              BATCH_NUM = 20
              BATCH_SIZE = 16
              EPOCH_NUM = 4
  
              IMAGE_SIZE = 784
              CLASS_NUM = 10
  
              # define a random dataset
              class RandomDataset(Dataset):
                  def __init__(self, num_samples):
                      self.num_samples = num_samples
  
                  def __getitem__(self, idx):
                      image = np.random.random([IMAGE_SIZE]).astype('float32')
                      label = np.random.randint(0, CLASS_NUM - 1, (1, )).astype('int64')
                      return image, label
  
                  def __len__(self):
                      return self.num_samples
  
              dataset = RandomDataset(BATCH_NUM * BATCH_SIZE)
  
              class SimpleNet(nn.Layer):
                  def __init__(self):
                      super(SimpleNet, self).__init__()
                      self.fc = nn.Linear(IMAGE_SIZE, CLASS_NUM)
  
                  def forward(self, image, label=None):
                      return self.fc(image)
  
              simple_net = SimpleNet()
              opt = paddle.optimizer.SGD(learning_rate=1e-3,
                                        parameters=simple_net.parameters())
  
              loader = DataLoader(dataset,
                                  batch_size=BATCH_SIZE,
                                  shuffle=True,
                                  drop_last=True,
                                  num_workers=2)
  
              for e in range(EPOCH_NUM):
                  for i, (image, label) in enumerate(loader()):
                      out = simple_net(image)
                      loss = F.cross_entropy(out, label)
                      avg_loss = paddle.mean(loss)
                      avg_loss.backward()
                      opt.minimize(avg_loss)
                      simple_net.clear_gradients()
                      print("Epoch {} batch {}: loss = {}".format(e, i, np.mean(loss.numpy())))
  
  
      .. note::
          For reading iterable dataset with multiprocess Dataloader,
          please see :code:`paddle.io.IterableDataset`
  
      """
  
      def __init__(self,
                   dataset,
                   feed_list=None,
                   places=None,
                   return_list=True,
                   batch_sampler=None,
                   batch_size=1,
                   shuffle=False,
                   drop_last=False,
                   collate_fn=None,
                   num_workers=0,
                   use_buffer_reader=True,
                   use_shared_memory=True,
                   timeout=0,
                   worker_init_fn=None,
                   persistent_workers=False):
          self.return_list = return_list
          self.collate_fn = collate_fn
          self.use_buffer_reader = use_buffer_reader
          self.worker_init_fn = worker_init_fn
  
          self.dataset = dataset
  
          if not return_list and not in_dygraph_mode():
              assert feed_list is not None, \
                      "feed_list should be set when return_list=False"
          self.feed_list = feed_list
  
          if places is None:
              places = _current_expected_place()
          if isinstance(places, (list, tuple)):
              places = _get_paddle_place_list(places)
          else:
              places = _get_paddle_place(places)
          self.places = _convert_places(places)
  
          assert num_workers >= 0, "num_workers should be a non-negative value"
          if num_workers > 0 and (sys.platform == 'darwin' or
                                  sys.platform == 'win32'):
              warnings.warn(
                  "DataLoader with multi-process mode is not supported on MacOs and Windows currently." \
                  " Please use signle-process mode with num_workers = 0 instead")
              num_workers = 0
          self.num_workers = num_workers
  
          self.use_shared_memory = use_shared_memory
          if use_shared_memory and num_workers == 0:
              self.use_shared_memory = False
  
          assert timeout >= 0, "timeout should be a non-negative value"
          self.timeout = timeout
  
          if isinstance(dataset, IterableDataset):
              self.dataset_kind = _DatasetKind.ITER
              if shuffle:
                  raise ValueError(
                      "IterableDataset not support shuffle, but got shuffle={}".
                      format(shuffle))
              if batch_sampler is not None:
                  raise ValueError(
                      "IterableDataset expect unspecified batch_sampler")
          else:
              self.dataset_kind = _DatasetKind.MAP
  
          if batch_sampler is not None:
              assert batch_size == 1 and not shuffle and not drop_last, \
                  "batch_size/shuffle/drop_last should not be set when " \
                  "batch_sampler is given"
              self.batch_sampler = batch_sampler
              self.batch_size = None
          elif batch_size is None:
              self.batch_sampler = None
              self.batch_size = None
          else:
              assert batch_size > 0, \
                  "batch_size should be None or a positive value when " \
                  "batch_sampler is not given"
              self.batch_size = batch_size
              if isinstance(dataset, IterableDataset):
                  self.batch_sampler = _InfiniteIterableSampler(dataset,
                                                                batch_size)
              else:
                  self.batch_sampler = BatchSampler(
                      dataset=dataset,
                      batch_size=batch_size,
                      shuffle=shuffle,
                      drop_last=drop_last)
  
          self.drop_last = drop_last
          self.auto_collate_batch = self.batch_sampler is not None
  
          self.pin_memory = False
          if in_dygraph_mode():
              self.pin_memory = use_pinned_memory() or True
  
          self._persistent_workers = persistent_workers
          self._iterator = None
  
      def __len__(self):
          if self.dataset_kind == _DatasetKind.ITER:
              raise ValueError("length of IterableDataset not supported")
          else:
              if self.auto_collate_batch:
                  return len(self.batch_sampler)
              else:
                  return len(self.dataset)
  
      def __iter__(self):
          if self.num_workers == 0:
              return _DataLoaderIterSingleProcess(self)
          elif self._persistent_workers:
              if self._iterator is None:
                  self._iterator = _DataLoaderIterMultiProcess(self)
              else:
                  self._iterator._reset()
              return self._iterator
          else:
              return _DataLoaderIterMultiProcess(self)
  
      def __call__(self):
          return self.__iter__()
  
      @staticmethod
      def from_generator(feed_list=None,
                         capacity=None,
                         use_double_buffer=True,
                         iterable=True,
                         return_list=False,
                         use_multiprocess=False,
                         drop_last=True):
          """
          .. warning::
            This API will be deprecated in the future, it is recommended to use
            :code:`paddle.io.DataLoader` which supports multi-processes acceleration.
  
          .. note::
            **The framework ensures that the data loading order of DataLoader is exactly the same as the user-defined data source.**
  
          Create a DataLoader object for loading data from Python generator. 
          Data would be prefetched using Python thread and be pushed
          into a queue asynchronously.
  
          The created DataLoader object provides 3 methods to set the data source
          :code:`set_sample_generator` , :code:`set_sample_list_generator` and 
          :code:`set_batch_generator` . Please see the following example codes
          to know their usages.
          
          If iterable = True, the created DataLoader object is a Python generator
          object, which is iterable using for-range loop.
  
          If iterable = False, the created DataLoader object provides 
          :code:`start()` and :code:`reset()` method to control the data reading
          process.
  
          Args:  
              feed_list (list(Tensor)|tuple(Tensor)): feed Tensor list.
                  The Tensors should be created by :code:`fluid.data()`.
              capacity (int): capacity of the queue maintained in DataLoader.
                  The unit is batch number. Set larger capacity if your reader 
                  is fast. 
              use_double_buffer (bool): whether to use double_buffer_reader. 
                  If use_double_buffer=True, the DataLoader would prefetch next 
                  batch data asynchronously, so it would speed up data feeding 
                  and occupies a little more CPU or GPU memory, i.e., the memory
                  of one batch input data. 
              iterable (bool): whether the created DataLoader is iterable. 
              return_list (bool): whether the return value on each device is 
                  presented as a list. It is only valid when iterable=True. 
                  If return_list=False, the return value on each device would 
                  be a dict of str -> LoDTensor, where the key of the dict is 
                  the name of each fed Tensors. If return_list=True, the 
                  return value on each device would be a list(LoDTensor). It is
                  recommended to use return_list=False in static graph mode and
                  use return_list=True in dygraph mode.  
              use_multiprocess (bool): whether to use multi-process to speed up
                  the data loading process in dygraph. Note: this parameter only
                  can be used in the dygraph mode. In the static graph mode,
                  whether this parameter is set or not has no effect.
                  The Default value is False.
              drop_last (bool): whether to drop the last batches whose number is
                  less than the CPU core/GPU card number. The default value is 
                  True. In training phase, users should not set drop_last=False,
                  because all CPU cores/GPU cards must read data from DataLoader. 
                  In inference phase, users can set drop_last=False, so that the
                  last batches whose number is less than the CPU core/GPU card
                  number can be tested. 
  
          Returns:
              loader (DataLoader): the created DataLoader object.
  
          Examples 1:
              
              .. code-block:: python
  
                  '''
                  Example in static graph mode
                  '''
                  import numpy as np
  
                  import paddle
                  import paddle.static as static
                  import paddle.nn.functional as F
  
  
                  BATCH_NUM = 10 
                  BATCH_SIZE = 16
                  EPOCH_NUM = 4
  
                  CLASS_NUM = 10
  
                  ITERABLE = True # whether the created DataLoader object is iterable
                  USE_GPU = False # whether to use GPU
  
                  DATA_FORMAT = 'batch_generator' # data format of data source user provides 
  
                  paddle.enable_static()
  
                  def simple_net(image, label):
                      fc_tmp = static.nn.fc(image, size=CLASS_NUM)
                      cross_entropy = F.softmax_with_cross_entropy(image, label)
                      loss = paddle.mean(cross_entropy)
                      sgd = paddle.optimizer.SGD(learning_rate=1e-3)
                      sgd.minimize(loss)
                      return loss
  
                  def get_random_images_and_labels(image_shape, label_shape):
                      image = np.random.random(size=image_shape).astype('float32')
                      label = np.random.random(size=label_shape).astype('int64')
                      return image, label
  
                  # If the data generator yields one sample each time,
                  # use DataLoader.set_sample_generator to set the data source.
                  def sample_generator_creator(): 
                      def __reader__():
                          for _ in range(BATCH_NUM * BATCH_SIZE):
                              image, label = get_random_images_and_labels([784], [1])
                              yield image, label
  
                      return __reader__
  
                  # If the data generator yield list of samples each time,
                  # use DataLoader.set_sample_list_generator to set the data source.
                  def sample_list_generator_creator():
                      def __reader__():
                          for _ in range(BATCH_NUM): 
                              sample_list = []
                              for _ in range(BATCH_SIZE):
                                  image, label = get_random_images_and_labels([784], [1])
                                  sample_list.append([image, label])
  
                              yield sample_list
  
                      return __reader__ 
  
                  # If the data generator yields a batch each time, 
                  # use DataLoader.set_batch_generator to set the data source.
                  def batch_generator_creator():
                      def __reader__():
                          for _ in range(BATCH_NUM):
                              batch_image, batch_label = get_random_images_and_labels([BATCH_SIZE, 784], [BATCH_SIZE, 1]) 
                              yield batch_image, batch_label
  
                      return __reader__
  
                  # If DataLoader is iterable, use for loop to train the network 
                  def train_iterable(exe, prog, loss, loader):
                      for _ in range(EPOCH_NUM):
                          for data in loader():
                              exe.run(prog, feed=data, fetch_list=[loss])
  
                  # If DataLoader is not iterable, use start() and reset() method to control the process 
                  def train_non_iterable(exe, prog, loss, loader):
                      for _ in range(EPOCH_NUM):
                          loader.start() # call DataLoader.start() before each epoch starts
                          try:
                              while True:
                                  exe.run(prog, fetch_list=[loss])
                          except paddle.core.EOFException:
                              loader.reset() # call DataLoader.reset() after catching EOFException 
  
                  def set_data_source(loader, places):
                      if DATA_FORMAT == 'sample_generator':
                          loader.set_sample_generator(sample_generator_creator(), batch_size=BATCH_SIZE, drop_last=True, places=places)
                      elif DATA_FORMAT == 'sample_list_generator':
                          loader.set_sample_list_generator(sample_list_generator_creator(), places=places)
                      elif DATA_FORMAT == 'batch_generator':
                          loader.set_batch_generator(batch_generator_creator(), places=places)
                      else:
                          raise ValueError('Unsupported data format')
  
                  image = static.data(name='image', shape=[None, 784], dtype='float32')
                  label = static.data(name='label', shape=[None, 1], dtype='int64')
  
                  # Define DataLoader 
                  loader = paddle.io.DataLoader.from_generator(feed_list=[image, label], capacity=16, iterable=ITERABLE)
  
                  # Define network
                  loss = simple_net(image, label)
  
                  # Set data source of DataLoader
                  #
                  # If DataLoader is iterable, places must be given and the number of places must be the same with device number.  
                  #  - If you are using GPU, call `paddle.static.cuda_places()` to get all GPU places. 
                  #  - If you are using CPU, call `paddle.static.cpu_places()` to get all CPU places. 
                  # 
                  # If DataLoader is not iterable, places can be None.
                  places = static.cuda_places() if USE_GPU else static.cpu_places()
                  set_data_source(loader, places)
  
                  exe = static.Executor(places[0])
                  exe.run(static.default_startup_program())
  
                  prog = static.CompiledProgram(static.default_main_program()).with_data_parallel(loss_name=loss.name)
  
                  if loader.iterable:
                      train_iterable(exe, prog, loss, loader)
                  else:
                      train_non_iterable(exe, prog, loss, loader)
  
  
          Examples 2:
  
              .. code-block:: python
  
                  '''
                  Example in dynamic graph mode. 
                  '''
                  import numpy as np
  
                  import paddle
                  import paddle.nn as nn
                  import paddle.optimizer as opt
                  import paddle.distributed as dist
  
                  BATCH_SIZE = 16
                  BATCH_NUM = 4
                  EPOCH_NUM = 4
  
                  IMAGE_SIZE = 784
                  CLASS_NUM = 10
  
                  USE_GPU = False # whether to use GPU
  
                  def _get_random_images_and_labels(image_shape, label_shape):
                          image = np.random.random(size=image_shape).astype('float32')
                          label = np.random.random(size=label_shape).astype('int64')
                          return image, label
  
                  def __reader__():
                          for _ in range(BATCH_NUM):
                              batch_image, batch_label = _get_random_images_and_labels(
                                  [BATCH_SIZE, IMAGE_SIZE], [BATCH_SIZE, CLASS_NUM])
                              yield batch_image, batch_label
  
                  def random_batch_reader():
                      return __reader__
  
                  class LinearNet(nn.Layer):
                      def __init__(self):
                          super(LinearNet, self).__init__()
                          self._linear = nn.Linear(IMAGE_SIZE, CLASS_NUM)
  
                      @paddle.jit.to_static
                      def forward(self, x):
                          return self._linear(x)
  
                  # set device
                  paddle.set_device('gpu' if USE_GPU else 'cpu')
  
                  # create network
                  layer = LinearNet()
                  dp_layer = paddle.DataParallel(layer)
                  loss_fn = nn.CrossEntropyLoss()
                  adam = opt.Adam(learning_rate=0.001, parameters=dp_layer.parameters())
  
                  # create data loader
                  loader = paddle.io.DataLoader.from_generator(capacity=5)
                  loader.set_batch_generator(random_batch_reader())
  
                  for epoch_id in range(EPOCH_NUM):
                      for batch_id, (image, label) in enumerate(loader()):
                          out = layer(image)
                          loss = loss_fn(out, label)
  
                          loss.backward()
  
                          adam.step()
                          adam.clear_grad()
                          print("Epoch {} batch {}: loss = {}".format(
                              epoch_id, batch_id, np.mean(loss.numpy())))
  
          Examples 3:
  
              .. code-block:: python
  
                  '''
                  Example of `drop_last` using in static graph multi-cards mode
                  '''
                  import paddle
                  import paddle.static as static
                  import numpy as np
                  import os
  
                  # We use 2 CPU cores to run inference network 
                  os.environ['CPU_NUM'] = '2'
  
                  paddle.enable_static()
  
                  # The data source has only 3 batches, which can not be
                  # divided evenly to each CPU core
                  def batch_generator():  
                      for i in range(3):
                          yield np.array([i+1]).astype('float32'), 
  
                  x = static.data(name='x', shape=[None], dtype='float32')  
                  y = x * x
  
                  def run_inference(drop_last): 
                      loader = paddle.io.DataLoader.from_generator(feed_list=[x],
                              capacity=8, drop_last=drop_last)
                      loader.set_batch_generator(batch_generator, static.cpu_places())
  
                      exe = static.Executor(paddle.CPUPlace())
                      prog = static.CompiledProgram(static.default_main_program())
                      prog = prog.with_data_parallel()
  
                      result = []
                      for data in loader():
                          each_ret, = exe.run(prog, feed=data, fetch_list=[y])
                          result.extend(each_ret)
                      return result
  
                  # Set drop_last to True, so that the last batch whose
                  # number is less than CPU core number would be discarded.
                  print(run_inference(drop_last=True)) # [1.0, 4.0]
  
                  # Set drop_last to False, so that the last batch whose
                  # number is less than CPU core number can be tested.
                  print(run_inference(drop_last=False)) # [1.0, 4.0, 9.0]
          """
          if in_dygraph_mode():
              return DygraphGeneratorLoader(feed_list, capacity,
                                            use_double_buffer, iterable,
                                            return_list, use_multiprocess)
          else:
              return GeneratorLoader(feed_list, capacity, use_double_buffer,
                                     iterable, return_list, drop_last)
  
      @staticmethod
      def from_dataset(dataset, places, drop_last=True):
          """
          .. warning::
            This API will be deprecated in the future, it is recommended to use
            :code:`paddle.io.DataLoader` which supports multi-processes acceleration.
  
          Create an iterable DataLoader object for loading data from Dataset.    
          Dataset is only supported in Linux system currently.
  
          Args:
              dataset (InMemoryDataset|QueueDataset): the dataset object.
              places (list(CUDAPlace)|list(CPUPlace)|list(str)): places where the result 
                  data should be converted. If places is list of string, the string in the list 
                  can be ``cpu``, ``gpu:x`` and ``gpu_pinned``, where x is the index of the GPUs.   
              drop_last (bool): whether to drop the last batch whose sample 
                  number is less than batch size. If drop_last = True, they
                  would be dropped. If drop_last = False, they would be kept. 
  
          Returns:
              loader (DataLoader): the created DataLoader object, which can be 
                  treated as a Python generator.   
  
          Examples:
  
              .. code-block:: python
  
                  import paddle
                  import paddle.static as static
  
                  paddle.enable_static()
  
                  image = static.data(name='image', shape=[None, 784], dtype='float32')
                  label = static.data(name='label', shape=[None, 1], dtype='int64')
  
                  dataset = paddle.distributed.QueueDataset()
                  dataset.init(
                      batch_size=32,
                      pipe_command='cat',
                      use_var=[image, label])
                  dataset.set_filelist(['a.txt', 'b.txt', 'c.txt'])
  
                  loader = paddle.io.DataLoader.from_dataset(dataset, static.cpu_places())
          """
          return DatasetLoader(dataset, places, drop_last)
  
  
  class DygraphGeneratorLoader(DataLoaderBase):
      """
      The GeneratorLoader of dygraph
  
      The multiprocess dygraph GeneratorLoader's most functions are different from 
      static graph GeneratorLoader, Separate implementation to keep code readable.
      """
  
      def __init__(self,
                   feed_list=None,
                   capacity=None,
                   use_double_buffer=True,
                   iterable=True,
                   return_list=True,
                   use_multiprocess=False):
          self._batch_reader = None
          self._places = None
          self._feed_list = feed_list
  
          if not capacity:
              raise ValueError("Please give value to capacity.")
          self._capacity = capacity
          self._use_double_buffer = use_double_buffer
  
          if not iterable:
              warnings.warn(
                  "Please NOTE: DygraphGeneratorLoader supports iterable mode only. Change to iterable mode."
              )
          self._iterable = True
          if not return_list:
              warnings.warn(
                  "Please NOTE: DygraphGeneratorLoader supports returning as list only. Change to return as list."
              )
          self._return_list = True
  
          # NOTE: the multiprocessing in different platform is incompatible, we will solve it later
          self._use_multiprocess = use_multiprocess
          if self._use_multiprocess and (sys.platform == 'darwin' or
                                         sys.platform == 'win32'):
              warnings.warn(
                  "NOTE: DygraphGeneratorLoader with multiprocess mode is not currently supported on MacOs and Windows."
              )
              self._use_multiprocess = False
  
          if self._use_multiprocess:
              # NOTE: the multiprocessing.Queue used to save loading data in self._process
              self._data_queue = None
              # NOTE: this process is used to load data asynchronously from self._batch_reader
              self._process = None
  
          # NOTE: the C++ LoDTensorBlockingQueue instance
          self._blocking_queue = None
          # NOTE: 1. In multiprocess mode, this thread is used to get next batch data from
          # self._data_queue, then push it into self._blocking_queue; 2. In singleprocess
          # mode, this thread is used to get next batch data from self._batch_reader, then 
          # push it into self._blocking_queue
          self._thread = None
          self._pin_memory = True if use_pinned_memory(
          ) is None else use_pinned_memory()
  
      @property
      def queue(self):
          return self._blocking_queue
  
      @property
      def iterable(self):
          return self._iterable
  
      def _clear_and_remove_data_queue(self):
          if self._data_queue is not None:
              while True:
                  try:
                      self._data_queue.get_nowait()
                  except queue.Empty:
                      break
              global multiprocess_queue_set
              multiprocess_queue_set.remove(self._data_queue)
  
      def _wait_thread_ends(self):
          thread = self._thread
          if thread is not None:
              self._blocking_queue.close()
              thread.join()
  
      def _wait_process_ends(self):
          process = self._process
          if process is not None:
              process.join()
              # erase process id
              core._erase_process_pids(id(self))
  
      def _init_iterable(self):
          self._wait_thread_ends()
          if self._use_multiprocess:
              self._wait_process_ends()
          self._var_names = []
          self._shapes = []
          self._dtypes = []
          self._need_check_feed = []
          self._blocking_queue = core.init_lod_tensor_blocking_queue(
              core.Variable(), self._capacity, False)
          self._reader = None
          self._reader = core.create_py_reader(
              self.queue, self._var_names, self._shapes, self._dtypes,
              self._need_check_feed, self._places, self._use_double_buffer, True,
              self._pin_memory)
  
      def _start(self):
          if self._use_multiprocess:
              # clear old _data_queue and remove it from multiprocess_queue_set
              self._clear_and_remove_data_queue()
              # set data_queue and process
              self._data_queue = multiprocessing.Queue(self._capacity)
              # add _data_queue into global queue set
              global multiprocess_queue_set
              multiprocess_queue_set.add(self._data_queue)
              self._process = multiprocessing.Process(
                  target=_reader_process_loop,
                  args=(self._batch_reader, self._data_queue))
              self._process.daemon = True
              self._process.start()
  
              # Set child process signal handler
              # NOTE: [ avoiding hang ] 1. if the child process dies due to bus error/segfault
              # or just hang, the main process will hang waiting for data, so here need to deal 
              # with SIGSEGV and SIGBUS of child process; 2. if the main process end before child
              # process, it shuts the all its daemonic children down with a SIGTERM (instead of 
              # joining them without a timeout), so here nedd to deal with SIGTERM.
              core._set_process_pids(id(self), [self._process.pid])
              _set_SIGCHLD_handler()
  
              # Set reader_thread
              self._thread_done_event = threading.Event()
              self._thread = threading.Thread(
                  target=self._reader_thread_loop_for_multiprocess,
                  args=(_current_expected_place(), ))
              self._thread.daemon = True
              self._thread.start()
          else:
              self._thread = threading.Thread(
                  target=self._reader_thread_loop_for_singleprocess,
                  args=(_current_expected_place(), ))
              self._thread.daemon = True
              self._thread.start()
  
      def _reset(self):
          self._reader.reset()
          self._wait_thread_ends()
          if self._use_multiprocess:
              self._wait_process_ends()
  
      def __iter__(self):
          assert self.iterable, "DataLoader is not iterable"
          assert self._batch_reader is not None, \
              "Data source of DataLoader has not set yet"
  
          self._init_iterable()
          self._start()
          return self
  
      def __next__(self):
          try:
              if _in_eager_mode():
                  return core.eager.read_next_tensor_list(
                      self._reader.read_next_list()[0])
              else:
                  return self._reader.read_next_var_list()
          except StopIteration:
              self._reset()
              six.reraise(*sys.exc_info())
  
      def _exit_thread_expectedly(self):
          self._thread_done_event.set()
          self._blocking_queue.close()
  
      def _exit_thread_unexpectedly(self):
          self._thread_done_event.set()
          self._blocking_queue.kill()
          logging.error("DataLoader reader thread raised an exception!")
  
      def _reader_thread_loop_for_multiprocess(self, legacy_expected_place):
          # See _DataLoaderIterSingleProcess._thread_loop() for why set expected place here.
          _set_expected_place(legacy_expected_place)
  
          while not self._thread_done_event.is_set():
              try:
                  # NOTE: [ avoid hanging ] Even with carefully designed data dependencies 
                  # (i.e., a put() always corresponding to a get()), hanging on get() can 
                  # still happen when data in queue is corrupted (e.g., due to 
                  # Queue.cancel_join_thread or unexpected exit). So we set a timeout whenever 
                  # we try to get data from `data_queue`
                  # NOTE: [ avoid failed quickly ] Here, the time setting of QUEUE_GET_TIMEOUT
                  # is relatively long, currently it is 60 seconds, because in some models,
                  # if the reader child process starts with a heavy burden, the child process
                  # has no enough time to put the data in the queue when the main process
                  # start trying to get data from queue. At this time, the child thread needs
                  # to wait slightly longer
                  tensor_list = self._data_queue.get(timeout=QUEUE_GET_TIMEOUT)
              except:
                  # NOTE [ avoid handing ] After adding the shared memory mechanism, not only
                  # the queue.Empty exception will occur here, but other exceptions will also
                  # occur, such as mmap failure. If it is not handled here, it will hang.
                  self._exit_thread_unexpectedly()
                  logging.error(
                      "DataLoader reader thread failed to read data from the multiprocessing.Queue."
                  )
                  six.reraise(*sys.exc_info())
  
              if not self._thread_done_event.is_set():
                  if tensor_list is not None:
                      try:
                          array = core.LoDTensorArray()
                          for tensor in tensor_list:
                              array.append(tensor)
                          if not self._blocking_queue.push(array):
                              self._blocking_queue.close()
                      except:
                          self._exit_thread_unexpectedly()
                          six.reraise(*sys.exc_info())
                  else:
                      self._exit_thread_expectedly()
  
      def _reader_thread_loop_for_singleprocess(self, legacy_expected_place):
          try:
              # See _DataLoaderIterSingleProcess._thread_loop() for why set expected place here.
              _set_expected_place(legacy_expected_place)
  
              for sample in self._batch_reader():
                  array = core.LoDTensorArray()
                  for item in sample:
                      if not isinstance(item, core.LoDTensor):
                          item = self._check_input_array(item)
                          tmp = core.LoDTensor()
                          tmp.set(item, core.CPUPlace())
                          item = tmp
  
                      array.append(item)
  
                  if not self._blocking_queue.push(array):
                      break
  
              self._blocking_queue.close()
              self._thread = None
          except Exception:
              self._blocking_queue.kill()
              self._thread = None
              logging.warning(
                  "DygraphDataLoader reader thread raised an exception.")
              six.reraise(*sys.exc_info())
  
      def set_sample_generator(self,
                               reader,
                               batch_size,
                               drop_last=True,
                               places=None):
          assert batch_size > 0, "batch_size must be larger than 0"
          if isinstance(places, (list, tuple)):
              places = _get_paddle_place_list(places)
          else:
              places = _get_paddle_place(places)
          self.set_sample_list_generator(
              paddle.batch(
                  reader, batch_size=batch_size, drop_last=drop_last),
              places=places)
          return self
  
      def set_sample_list_generator(self, reader, places=None):
          if isinstance(places, (list, tuple)):
              places = _get_paddle_place_list(places)
          else:
              places = _get_paddle_place(places)
  
          def __batch_reader_impl__():
              for batch in reader():
                  slots = []
                  for items in batch:
                      for i, item in enumerate(items):
                          if len(slots) < len(items):
                              slots.append([item])
                          else:
                              slots[i].append(item)
                  yield slots
  
          self.set_batch_generator(__batch_reader_impl__, places)
          return self
  
      def set_batch_generator(self, reader, places=None):
          if isinstance(places, (list, tuple)):
              places = _get_paddle_place_list(places)
          else:
              places = _get_paddle_place(places)
          self._batch_reader = reader
          if places is None:
              places = _current_expected_place()
          self._places = _convert_places(places)
          assert len(self._places) == 1, \
              "Number of places must be 1 in imperative mode"
          return self
  
  
  class GeneratorLoader(DataLoaderBase):
      def __init__(self,
                   feed_list=None,
                   capacity=None,
                   use_double_buffer=True,
                   iterable=True,
                   return_list=False,
                   drop_last=True):
          self._tensor_reader = None
          self._places = None
          self._thread = None
          self._queue = None
          self._feed_list = feed_list
          self._exited = False
          self._drop_last = drop_last
          self._keep_order = keep_data_loader_order()
          if not capacity:
              raise ValueError("Please give value to capacity.")
          self._iterable = iterable
          self._return_list = return_list
          if not self._feed_list:
              raise Exception("Feed list must be given under static mode.")
          self._use_double_buffer = use_double_buffer
          self._capacity = capacity
          if not self._iterable:
              self._init_non_iterable()
  
      def _wait_thread_ends(self):
          # Get self._thread first to prevent data race, because __thread_main__
          # would set self._thread be None at the end
          thread = self._thread
          if thread is not None and self._iterable:
              self._queue.close()
              thread.join()
  
      def _init_iterable(self):
          self._wait_thread_ends()
          self._var_names = [v.name for v in self._feed_list]
          self._shapes = [v.shape for v in self._feed_list]
          self._dtypes = [v.dtype for v in self._feed_list]
          self._need_check_feed = [
              v.desc.need_check_feed() for v in self._feed_list
          ]
          self._queue = core.init_lod_tensor_blocking_queue(
              core.Variable(), self._capacity, self._keep_order)
          self._reader = None
          self._reader = core.create_py_reader(
              self.queue, self._var_names, self._shapes, self._dtypes,
              self._need_check_feed, self._places, self._use_double_buffer,
              self._drop_last, False)
  
      def _init_non_iterable(self):
          lod_levels = []
          dtypes = []
          shape_concat = []
          ranks = []
          shapes = []
          need_check_feed = []
  
          for feed_data in self._feed_list:
              dtypes.append(feed_data.dtype)
              shape_concat.extend(feed_data.shape)
              ranks.append(len(feed_data.shape))
              shapes.append(feed_data.shape)
              lod_levels.append(feed_data.lod_level)
              need_check_feed.append(int(feed_data.desc.need_check_feed()))
  
          queue_name = data_loader_unique_name_generator(
              'lod_tensor_blocking_queue')
          reader_name = data_loader_unique_name_generator('create_py_reader')
          double_buffer_name = data_loader_unique_name_generator('double_buffer')
  
          var = global_scope().var(queue_name)
          self._queue = core.init_lod_tensor_blocking_queue(var, self._capacity,
                                                            self._keep_order)
  
          if self._keep_order:
              block = default_main_program().current_block()
          else:
              block = default_startup_program().current_block()
  
          reader_var = block.create_var(name=reader_name)
  
          dtype_int = [int(t) for t in dtypes]
          block.append_op(
              type='create_py_reader',
              inputs={'blocking_queue': [queue_name]},
              outputs={'Out': [reader_var]},
              attrs={
                  'shape_concat': shape_concat,
                  'lod_levels': lod_levels,
                  'dtypes': dtype_int,
                  'need_check_feed': need_check_feed,
                  'ranks': ranks
              })
  
          reader_var.desc.set_dtypes(dtypes)
          reader_var.persistable = True
          reader_var.stop_gradient = True
  
          if self._keep_order:
              main_prog_var = reader_var
              reader = main_prog_var
              reader.reset = self._queue.reset
          else:
              main_prog_var = _copy_reader_var_(
                  default_main_program().current_block(), reader_var)
  
              main_prog_var.stop_gradient = True
              main_prog_var.persistable = True
  
              reader = monkey_patch_reader_methods(main_prog_var)
  
          if self._use_double_buffer:
              double_buffer_reader = double_buffer(
                  reader, name=double_buffer_name)
              # we return a double buffer reader. However, the reset method comes from
              # py_reader.
              double_buffer_reader.reset = reader.reset
              reader = double_buffer_reader
  
          self._reader = reader
  
          default_main_program().current_block().append_op(
              type='read',
              inputs={'Reader': [self._reader]},
              outputs={'Out': self._feed_list},
              attrs={'drop_last': self._drop_last})
  
      @property
      def queue(self):
          return self._queue
  
      @property
      def iterable(self):
          return self._iterable
  
      def __iter__(self):
          assert self.iterable, "DataLoader is not iterable"
          assert self._tensor_reader is not None, \
              "Data source of DataLoader has not set yet"
  
          self._init_iterable()
          self._start()
          return self
  
      def __next__(self):
          try:
              if self._return_list:
                  data = self._reader.read_next_list()
                  for i in range(len(data)):
                      data[i] = data[i]._move_to_list()
                  return data
              else:
                  return self._reader.read_next()
          except StopIteration:
              self._queue.close()
              self._reset()
              six.reraise(*sys.exc_info())
  
      def start(self):
          assert not self._iterable, "start() cannot be called when DataLoader is iterable"
          self._start()
  
      def reset(self):
          assert not self._iterable, "reset() cannot be called when DataLoader is iterable"
          self._reset()
  
      def _start(self):
          def __thread_main__(legacy_expected_place):
              try:
                  # See _DataLoaderIterSingleProcess._thread_loop() for why set expected place here.
                  _set_expected_place(legacy_expected_place)
  
                  while not self._queue.wait_for_inited(1):
                      if self._exited:
                          return
  
                  for tensors in self._tensor_reader():
                      array = core.LoDTensorArray()
                      for item in tensors:
                          if not isinstance(item, core.LoDTensor):
                              item = self._check_input_array(item)
                              tmp = core.LoDTensor()
                              tmp.set(item, core.CPUPlace())
                              item = tmp
  
                          array.append(item)
  
                      if not self._queue.push(array):
                          break
  
                  self._queue.close()
                  self._thread = None
              except Exception as ex:
                  self._queue.kill()
                  self._thread = None
                  logging.warning('Your reader has raised an exception!')
                  six.reraise(*sys.exc_info())
  
          self._thread = threading.Thread(
              target=__thread_main__, args=(_current_expected_place(), ))
          self._thread.daemon = True
          self._thread.start()
  
      def _reset(self):
          self._queue.close()
          self._exited = True
          thread = self._thread
          if thread is not None:
              thread.join()
  
          self._exited = False
          self._reader.reset()
  
      def set_sample_generator(self,
                               reader,
                               batch_size,
                               drop_last=True,
                               places=None):
          assert batch_size > 0, "batch_size must be larger than 0"
          if isinstance(places, (list, tuple)):
              places = _get_paddle_place_list(places)
          else:
              places = _get_paddle_place(places)
          has_lod = False
          for f in self._feed_list:
              if f.lod_level != 0:
                  has_lod = True
                  break
  
          if has_lod:
              self.set_sample_list_generator(
                  paddle.batch(
                      reader, batch_size=batch_size, drop_last=drop_last),
                  places=places)
          else:
              reader = BatchedTensorProvider(
                  feed_list=self._feed_list,
                  place=core.CPUPlace(),
                  batch_size=batch_size,
                  generator=reader,
                  drop_last=drop_last)
              self.set_batch_generator(reader, places=places)
          return self
  
      def set_sample_list_generator(self, reader, places=None):
          if isinstance(places, (list, tuple)):
              places = _get_paddle_place_list(places)
          else:
              places = _get_paddle_place(places)
          with program_guard(Program(), Program()):
              feeder = DataFeeder(
                  feed_list=self._feed_list, place=core.CPUPlace())
              paddle_reader = feeder.decorate_reader(reader, multi_devices=False)
  
          def __tensor_reader_impl__():
              for slots in paddle_reader():
                  yield [slots[var.name] for var in self._feed_list]
  
          self.set_batch_generator(__tensor_reader_impl__, places)
          return self
  
      def set_batch_generator(self, reader, places=None):
          if isinstance(places, (list, tuple)):
              places = _get_paddle_place_list(places)
          else:
              places = _get_paddle_place(places)
          self._tensor_reader = reader
          if self._iterable:
              assert places is not None, "Places cannot be None when DataLoader is iterable"
              self._places = _convert_places(places)
          else:
              if places is not None:
                  logging.info(
                      'places would be ommited when DataLoader is not iterable')
          return self
  
  
  class PyReader(DataLoaderBase):
      r"""
      Create a reader object for data feeding in Python. 
      Data would be prefetched using Python thread and be pushed
      into a queue asynchronously. Data in the queue would be extracted 
      automatically when `Executor.run(...)` is called.
  
      Args:  
          feed_list (list(Variable)|tuple(Variable)): feed variable list.
              The variables should be created by :code:`fluid.layers.data()`.
          capacity (int): capacity of the queue maintained in PyReader.
              The unit is batch number. Set larger capacity if your reader 
              is fast. 
          use_double_buffer (bool): whether to use double_buffer_reader. 
              If use_double_buffer=True, PyReader would prefetch next 
              batch data asynchronously, so it would speed up data feeding 
              and occupies a little more CPU or GPU memory, i.e., the memory
              of one batch input data. 
          iterable (bool): whether the created PyReader is iterable. 
          return_list (bool): whether the return value on each device is 
              presented as a list. It is only valid when iterable=True. 
              If return_list=False, the return value on each device would 
              be a dict of str -> LoDTensor, where the key of the dict is 
              the name of each fed variables. If return_list=True, the 
              return value on each device would be a list(LoDTensor). It is
              recommended to use return_list=False in static graph mode and
              use return_list=True in dygraph mode. 
  
      Returns:
          the created reader object.
  
      Return type:
          reader(Reader)
  
      Examples:
          1. If iterable = False, the created PyReader object is almost the
             same as :code:`fluid.layers.py_reader()`. Operators would be 
             inserted into the program. User should call :code:`start()` 
             before each epoch and catch :code:`fluid.core.EOFException`
             thrown by :code:`Executor.run()` when epoch ends. Once the 
             exception is caught, user should call :code:`reset()` to reset 
             the reader manually.
  
          .. code-block:: python
  
             import paddle
             import paddle.fluid as fluid
             import numpy as np
  
             EPOCH_NUM = 3
             ITER_NUM = 5
             BATCH_SIZE = 3
             
             def network(image, label):
                 # User-defined network, here is an example of softmax regression.
                 predict = fluid.layers.fc(input=image, size=10, act='softmax')           
                 return fluid.layers.cross_entropy(input=predict, label=label)
  
             def reader_creator_random_image_and_label(height, width):
                 def reader():
                     for i in range(ITER_NUM):
                         fake_image = np.random.uniform(low=0,
                                                        high=255,
                                                        size=[height, width])
                         fake_label = np.ones([1])
                         yield fake_image, fake_label
                 return reader
  
             image = fluid.data(name='image', shape=[None, 784, 784], dtype='float32')
             label = fluid.data(name='label', shape=[None, 1], dtype='int64')
  
             reader = fluid.io.PyReader(feed_list=[image, label],
                                        capacity=4,
                                        iterable=False)
  
             user_defined_reader = reader_creator_random_image_and_label(784, 784)
             reader.decorate_sample_list_generator(
                 paddle.batch(user_defined_reader, batch_size=BATCH_SIZE))
             loss = network(image, label)
             executor = fluid.Executor(fluid.CPUPlace())
             executor.run(fluid.default_startup_program())
             for i in range(EPOCH_NUM):
                 reader.start()
                 while True:
                     try:
                         executor.run(feed=None)
                     except fluid.core.EOFException:
                         reader.reset()
                         break
  
   
          2. If iterable=True, the created PyReader object is decoupled with
             the program. No operator would be inserted into the program. 
             In this case, the created reader is a Python generator, which 
             is iterable. User should feed the data yielded from PyReader 
             object into :code:`Executor.run(feed=...)`.  
  
          .. code-block:: python
  
             import paddle
             import paddle.fluid as fluid
             import numpy as np
  
             EPOCH_NUM = 3
             ITER_NUM = 5
             BATCH_SIZE = 10
  
             def network(image, label):
                 # User-defined network, here is an example of softmax regression.
                 predict = fluid.layers.fc(input=image, size=10, act='softmax')           
                 return fluid.layers.cross_entropy(input=predict, label=label)
  
             def reader_creator_random_image(height, width):
                 def reader():
                     for i in range(ITER_NUM):
                         fake_image = np.random.uniform(low=0, high=255, size=[height, width])
                         fake_label = np.ones([1])
                         yield fake_image, fake_label 
                 return reader
  
             image = fluid.data(name='image', shape=[None, 784, 784], dtype='float32')
             label = fluid.data(name='label', shape=[None, 1], dtype='int64')
             reader = fluid.io.PyReader(feed_list=[image, label], capacity=4, iterable=True, return_list=False)
  
             user_defined_reader = reader_creator_random_image(784, 784)
             reader.decorate_sample_list_generator(
                 paddle.batch(user_defined_reader, batch_size=BATCH_SIZE),
                     fluid.core.CPUPlace())
             
             loss = network(image, label)
             executor = fluid.Executor(fluid.CPUPlace())
             executor.run(fluid.default_startup_program())
             
             for _ in range(EPOCH_NUM):
                 for data in reader():
                     executor.run(feed=data, fetch_list=[loss])
  
  
          3. If return_list=True, the return values would be presented as list instead of dict. 
             This is usually used in dygraph mode.
  
          .. code-block:: python
  
             import paddle
             import paddle.fluid as fluid
             import numpy as np
  
             ITER_NUM = 5
             BATCH_SIZE = 10
  
             def reader_creator_random_image(height, width):
                 def reader():
                     for i in range(ITER_NUM):
                         yield np.random.uniform(low=0, high=255, size=[height, width]), \
                             np.random.random_integers(low=0, high=9, size=[1])
                 return reader
  
             place = fluid.CPUPlace()
             with fluid.dygraph.guard(place):
                 py_reader = fluid.io.PyReader(capacity=2, return_list=True)
                 user_defined_reader = reader_creator_random_image(784, 784)
                 py_reader.decorate_sample_list_generator(
                     paddle.batch(user_defined_reader, batch_size=BATCH_SIZE),
                     place)
                 for image, label in py_reader():
                     relu = fluid.layers.relu(image)
      """
  
      def __init__(self,
                   feed_list=None,
                   capacity=None,
                   use_double_buffer=True,
                   iterable=True,
                   return_list=False):
          self._loader = DataLoader.from_generator(
              feed_list, capacity, use_double_buffer, iterable, return_list)
  
      @property
      def queue(self):
          return self._loader.queue
  
      @property
      def iterable(self):
          return self._loader.iterable
  
      def __iter__(self):
          return self._loader.__iter__()
  
      def __next__(self):
          return self._loader.__next__()
  
      def start(self):
          '''
          Start the data feeding thread. 
          Can only call when the reader object is not iterable.  
          
  	Example:
  	    .. code-block:: python
      
                  import paddle
                  import paddle.fluid as fluid
                  import numpy as np
  
                  BATCH_SIZE = 10
  
                  def generator():
                      for i in range(5):
                          yield np.random.uniform(low=0, high=255, size=[784, 784]),
  
                  image = fluid.data(name='image', shape=[None, 784, 784], dtype='float32')
                  reader = fluid.io.PyReader(feed_list=[image], capacity=4, iterable=False)
                  reader.decorate_sample_list_generator(
                      paddle.batch(generator, batch_size=BATCH_SIZE))
  
                  executor = fluid.Executor(fluid.CPUPlace())
                  executor.run(fluid.default_startup_program())
                  for i in range(3):
                      reader.start()
                      while True:
                          try:
                              executor.run(feed=None)
                          except fluid.core.EOFException:
                              reader.reset()
                              break
  
  	    '''
          self._loader.start()
  
      def reset(self):
          '''
          Reset the reader object when :code:`fluid.core.EOFException` raises. 
          Can only call when the reader object is not iterable.
          
          Example:
              .. code-block:: python
  
                  import paddle
                  import paddle.fluid as fluid
                  import numpy as np
  
                  BATCH_SIZE = 10
  
                  def generator():
                      for i in range(5):
                          yield np.random.uniform(low=0, high=255, size=[784, 784]),
  
                  image = fluid.data(name='image', shape=[None, 784, 784], dtype='float32')
                  reader = fluid.io.PyReader(feed_list=[image], capacity=4, iterable=False)
                  reader.decorate_sample_list_generator(
                      paddle.batch(generator, batch_size=BATCH_SIZE))
  
                  executor = fluid.Executor(fluid.CPUPlace())
                  executor.run(fluid.default_startup_program())
                  for i in range(3):
                      reader.start()
                      while True:
                          try:
                              executor.run(feed=None)
                          except fluid.core.EOFException:
                              reader.reset()
                              break        
  
          '''
          self._loader.reset()
  
      def decorate_sample_generator(self,
                                    sample_generator,
                                    batch_size,
                                    drop_last=True,
                                    places=None):
          '''
          Set the data source of the PyReader object.
          
          The provided :code:`sample_generator` should be a Python generator,
          which yields list(numpy.ndarray)-typed data of each sample.
  
          :code:`places` must be set when the PyReader object is iterable.
  
          If all inputs have no lods, this method is faster than 
          :code:`decorate_sample_list_generator(paddle.batch(sample_generator, ...))` .
  
          Args:
              sample_generator (generator): Python generator that yields
                  list(numpy.ndarray)-typed sample data.
              batch_size (int): batch size. Must be larger than 0.
              drop_last (bool): Whether to drop the last batch when sample number
                  is less than batch_size. 
              places (None|list(CUDAPlace)|list(CPUPlace)): place list. Must
                  be provided when PyReader is iterable.
  
          Example:
              .. code-block:: python
  
                  import paddle.fluid as fluid
                  import numpy as np
  
                  EPOCH_NUM = 3
                  ITER_NUM = 15
                  BATCH_SIZE = 3
          
                  def network(image, label):
                      # User-defined network, here is an example of softmax regression.
                      predict = fluid.layers.fc(input=image, size=10, act='softmax')           
                      return fluid.layers.cross_entropy(input=predict, label=label)
  
                  def random_image_and_label_generator(height, width):
                      def generator():
                          for i in range(ITER_NUM):
                              fake_image = np.random.uniform(low=0,
                                                             high=255,
                                                             size=[height, width])
                              fake_label = np.array([1])
                              yield fake_image, fake_label
                      return generator
  
                  image = fluid.data(name='image', shape=[None, 784, 784], dtype='float32')
                  label = fluid.data(name='label', shape=[None, 1], dtype='int64')
                  reader = fluid.io.PyReader(feed_list=[image, label], capacity=4, iterable=True)
  
                  user_defined_generator = random_image_and_label_generator(784, 784)
                  reader.decorate_sample_generator(user_defined_generator,
                                                   batch_size=BATCH_SIZE,
                                                   places=[fluid.CPUPlace()])
                  loss = network(image, label)
                  executor = fluid.Executor(fluid.CPUPlace())
                  executor.run(fluid.default_startup_program())
  
                  for _ in range(EPOCH_NUM):
                      for data in reader():
                          executor.run(feed=data, fetch_list=[loss])
      
          '''
          self._loader.set_sample_generator(sample_generator, batch_size,
                                            drop_last, places)
  
      def decorate_sample_list_generator(self, reader, places=None):
          '''
          Set the data source of the PyReader object. 
  
          The provided :code:`reader` should be a Python generator,
          which yields list(numpy.ndarray) typed batched data. 
          
          :code:`places` must be set when the PyReader object is iterable.
  
          Args:
              reader (generator): Python generator that yields 
                  list(numpy.ndarray)-typed batched data. 
              places (None|list(CUDAPlace)|list(CPUPlace)): place list. Must
                  be provided when PyReader is iterable.
          
          Example:
              .. code-block:: python
  
                  import paddle
                  import paddle.fluid as fluid
                  import numpy as np
  
                  EPOCH_NUM = 3
                  ITER_NUM = 15
                  BATCH_SIZE = 3
  
                  def network(image, label):
                      # User-defined network, here is an example of softmax regression.
                      predict = fluid.layers.fc(input=image, size=10, act='softmax')           
                      return fluid.layers.cross_entropy(input=predict, label=label)
  
                  def random_image_and_label_generator(height, width):
                      def generator():
                          for i in range(ITER_NUM):
                              fake_image = np.random.uniform(low=0,
                                                             high=255,
                                                             size=[height, width])
                              fake_label = np.ones([1])
                              yield fake_image, fake_label
                      return generator
  
                  image = fluid.data(name='image', shape=[None, 784, 784], dtype='float32')
                  label = fluid.data(name='label', shape=[None, 1], dtype='int64')
                  reader = fluid.io.PyReader(feed_list=[image, label], capacity=4, iterable=True)
  
                  user_defined_generator = random_image_and_label_generator(784, 784)
                  reader.decorate_sample_list_generator(
                      paddle.batch(user_defined_generator, batch_size=BATCH_SIZE),
                      fluid.core.CPUPlace())
                  
                  loss = network(image, label)
                  executor = fluid.Executor(fluid.core.CPUPlace())
                  executor.run(fluid.default_startup_program())
  
                  for _ in range(EPOCH_NUM):
                      for data in reader():
                          executor.run(feed=data, fetch_list=[loss])
                   
          '''
          self._loader.set_sample_list_generator(reader, places)
  
      def decorate_batch_generator(self, reader, places=None):
          '''
          Set the data source of the PyReader object.
  
          The provided :code:`reader` should be a Python generator,
          which yields numpy.ndarray-typed or LoDTensor-typed batched data.
  
          :code:`places` must be set when the PyReader object is iterable.
  
          Args:
              reader (generator): Python generator that yields LoDTensor-typed
                  batched data.
              places (None|list(CUDAPlace)|list(CPUPlace)): place list. Must
                  be provided when PyReader is iterable.
  
          Example:
              .. code-block:: python
  
                  import paddle.fluid as fluid
                  import numpy as np
  
                  EPOCH_NUM = 3
                  ITER_NUM = 15
                  BATCH_SIZE = 3
                 
                  def network(image, label):
                      # User-defined network, here is an example of softmax regression.
                      predict = fluid.layers.fc(input=image, size=10, act='softmax')           
                      return fluid.layers.cross_entropy(input=predict, label=label)
  
                  def random_image_and_label_generator(height, width):
                      def generator():
                          for i in range(ITER_NUM):
                              batch_image = np.random.uniform(low=0,
                                                              high=255,
                                                              size=[BATCH_SIZE, height, width])
                              batch_label = np.ones([BATCH_SIZE, 1])
                              batch_image = batch_image.astype('float32')
                              batch_label = batch_label.astype('int64')
                              yield batch_image, batch_label
                      return generator
  
                  image = fluid.data(name='image', shape=[None, 784, 784], dtype='float32')
                  label = fluid.data(name='label', shape=[None, 1], dtype='int64')
                  reader = fluid.io.PyReader(feed_list=[image, label], capacity=4, iterable=True)
  
                  user_defined_generator = random_image_and_label_generator(784, 784)
                  reader.decorate_batch_generator(user_defined_generator, fluid.CPUPlace())
                  
                  loss = network(image, label)
                  executor = fluid.Executor(fluid.CPUPlace())
                  executor.run(fluid.default_startup_program())
  
                  for _ in range(EPOCH_NUM):
                      for data in reader():
                          executor.run(feed=data, fetch_list=[loss])
  
          '''
          self._loader.set_batch_generator(reader, places)
  
  
  class DatasetLoader(DataLoaderBase):
      def __init__(self, dataset, places, drop_last):
          assert isinstance(dataset, paddle.distributed.fleet.dataset.
                            DatasetBase), "dataset must be type of DatasetBase"
          assert not in_dygraph_mode(
          ), "DatasetLoader is not supported in dygraph mode yet"
          if isinstance(places, (list, tuple)):
              places = _get_paddle_place_list(places)
          else:
              places = _get_paddle_place(places)
  
          thread_num = len(places)
  
          assert len(dataset.filelist) >= thread_num, \
              "Filelist number of dataset {} must be not less than place number {}".format(len(dataset.filelist), thread_num)
  
          if dataset.thread_num != 0 and dataset.thread_num != thread_num:
              logging.warn('thread_num {} which is set in Dataset is ignored'.
                           format(dataset.thread_num))
  
          dataset._set_thread(thread_num)
  
          if isinstance(dataset, paddle.distributed.fleet.dataset.
                        InMemoryDataset) and dataset.queue_num > thread_num:
              logging.warn("queue_num {} which is set in Dataset is ignored".
                           format(dataset.queue_num))
              dataset._set_queue_num(thread_num)
  
          self._dataset = dataset
          use_slots = [
              slot.name for slot in dataset.proto_desc.multi_slot_desc.slots
              if slot.is_used
          ]
  
          self._iterable_dataset = core.IterableDatasetWrapper(
              dataset.dataset, use_slots,
              _convert_places(places), dataset.proto_desc.batch_size, drop_last)
  
      def __iter__(self):
          self._dataset._finish_to_run()
          self._dataset._prepare_to_run()
          self._iterable_dataset._start()
          return self
  
      def __next__(self):
          return self._iterable_dataset._next()
  
apis: numpy.asarray