tensorflow2：tf.app.run()

# tensorflow/tensorflow/python/platform/default/_app.py  
  
# Copyright 2015 Google Inc. 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.  
# ==============================================================================  
  
"""Generic entry point script."""  
from __future__ import absolute_import  
from __future__ import division  
from __future__ import print_function  
  
import sys  
  
from tensorflow.python.platform import flags  
  
  
def run(main=None):  
  f = flags.FLAGS  
  f._parse_flags()  
  main = main or sys.modules[‘__main__‘].main  
  sys.exit(main(sys.argv))  

tf.app.flags.DEFINE_boolean("self_test", False, "True if running a self test.")  
tf.app.flags.DEFINE_boolean(‘use_fp16‘, False,  
                            "Use half floats instead of full floats if True.")  
FLAGS = tf.app.flags.FLAGS