# Copyright (c) 2016 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.

__all__ = []


def batch(reader, batch_size, drop_last=False):
 """
 This operator creates a batched reader which combines the data from the 
 input reader to batched data.

 Args:
 reader(generator): the data reader to read from.
 batch_size(int): size of each mini-batch.
 drop_last(bool, optional): If set to True, the last batch is dropped when 
 the size of last batch is not equal to batch_size, if set to False,
 it will not. Default: False.
 Returns:
 The batched reader. 

 Return Type:
 generator 

 Examples:
 .. code-block:: python

 import paddle
 def reader():
 for i in range(10):
 yield i
 batch_reader = paddle.batch(reader, batch_size=2)

 for data in batch_reader():
 print(data)

 # Output is
 # [0, 1]
 # [2, 3]
 # [4, 5]
 # [6, 7]
 # [8, 9]
 """

 def batch_reader():
 r = reader()
 b = []
 for instance in r:
 b.append(instance)
 if len(b) == batch_size:
 yield b
 b = []
 if drop_last is False and len(b) != 0:
 yield b

 # Batch size check
 batch_size = int(batch_size)
 if batch_size <= 0:
 raise ValueError("batch_size should be a positive integeral value, "
 "but got batch_size={}".format(batch_size))

 return batch_reader