refine reader to support paddle1.8 API and fix the code style

ppcls/data/reader.py

-#copyright (c) 2020 PaddlePaddle Authors. All Rights Reserve.
+# copyright (c) 2020 PaddlePaddle Authors. All Rights Reserve.
 #
-#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
+# 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.
+# 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.
 
-import cv2
 import numpy as np
+import imghdr
 import os
 import signal
 
-import paddle
+from paddle.fluid.io import multiprocess_reader
 
 from . import imaug
 from .imaug import transform
-from .imaug import MixupOperator
 from ppcls.utils import logger
 
 trainers_num = int(os.environ.get('PADDLE_TRAINERS_NUM', 1))
@@ -35,7 +34,7 @@ class ModeException(Exception):
 
     def __init__(self, message='', mode=''):
         message += "\nOnly the following 3 modes are supported: " \
-                "train, valid, test. Given mode is {}".format(mode)
+            "train, valid, test. Given mode is {}".format(mode)
         super(ModeException, self).__init__(message)
 
 
@@ -46,10 +45,10 @@ class SampleNumException(Exception):
 
     def __init__(self, message='', sample_num=0, batch_size=1):
         message += "\nError: The number of the whole data ({}) " \
-                "is smaller than the batch_size ({}), and drop_last " \
-                "is turnning on, so nothing  will feed in program, " \
-                "Terminated now. Please reset batch_size to a smaller " \
-                "number or feed more data!".format(sample_num, batch_size)
+            "is smaller than the batch_size ({}), and drop_last " \
+            "is turnning on, so nothing  will feed in program, " \
+            "Terminated now. Please reset batch_size to a smaller " \
+            "number or feed more data!".format(sample_num, batch_size)
         super(SampleNumException, self).__init__(message)
 
 
@@ -80,12 +79,12 @@ def check_params(params):
 
     data_dir = params.get('data_dir', '')
     assert os.path.isdir(data_dir), \
-            "{} doesn't exist, please check datadir path".format(data_dir)
+        "{} doesn't exist, please check datadir path".format(data_dir)
 
     if params['mode'] != 'test':
         file_list = params.get('file_list', '')
         assert os.path.isfile(file_list), \
-                "{} doesn't exist, please check file list path".format(file_list)
+            "{} doesn't exist, please check file list path".format(file_list)
 
 
 def create_file_list(params):
@@ -176,8 +175,8 @@ def partial_reader(params, full_lines, part_id=0, part_num=1):
         part_id(int): part index of the current partial data
         part_num(int): part num of the dataset
     """
-    assert part_id < part_num, ("part_num: {} should be larger " \
-            "than part_id: {}".format(part_num, part_id))
+    assert part_id < part_num, ("part_num: {} should be larger "
+                                "than part_id: {}".format(part_num, part_id))
 
     full_lines = full_lines[part_id::part_num]
 
@@ -216,11 +215,11 @@ def mp_reader(params):
     for part_id in range(part_num):
         readers.append(partial_reader(params, full_lines, part_id, part_num))
 
-    return paddle.reader.multiprocess_reader(readers, use_pipe=False)
+    return multiprocess_reader(readers, use_pipe=False)
 
 
 def term_mp(sig_num, frame):
-    """ kill all child processes 
+    """ kill all child processes
     """
     pid = os.getpid()
     pgid = os.getpgid(os.getpid())