丛零开始
看了一篇入门级的文章 Tensorflow学习笔记2：About Session, Graph, Operation and Tensor，讲的很简单，清楚，如果刚开始接触tensorflow看一下就会很明白怎么去跑一个最简单的网络，如下这种网络。
import tensorflow as tf
a = tf.constant(1)
b = tf.constant(2)
c = tf.constant(3)
d = tf.constant(4)
add1 = tf.add(a, b)
mul1 = tf.mul(b, c)
add2 = tf.add(c, d)
output = tf.add(add1, mul1)
with tf.Session() as sess:
print sess.run(output)
tensorflow可以有两种入口的方式
- session
- tf.app.run
session
一个Session可能会拥有一些资源，例如Variable或者Queue。当我们不再需要该session的时候，需要将这些资源进行释放。有两种方式，
1. 调用session.close()方法；
2. 使用with tf.Session()创建上下文（Context）来执行，当上下文退出时自动释放。
使用session的方式也很好理解，先建立图，再去定义变量，执行。
import tensorflow as tf
# Build a graph.
a = tf.constant([1.0, 2.0])
b = tf.constant([3.0, 4.0])
c = a * b
# Launch the graph in a session.
sess = tf.Session()
# Evaluate the tensor 'c'.
print sess.run(c)
sess.close()
# result: [3., 8.]
上面第二点提到可以创建上下文，这样的方式更有利于自动清理变量
import tensorflow as tf
# Build a graph.
a = tf.constant([1.0, 2.0])
b = tf.constant([3.0, 4.0])
c = a * b
with tf.Session() as sess:
print sess.run(c)
tf.app.run
看到很多源代码中都会出现
if __name__ == "__main__":
tf.app.run()
这样的代码其实是在执行解析flag后再去执行main函数，源代码如下
# 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))
在同一个python文件下，可以def一个main函数，run的时候就会去找这个main函数执行。
def main(unused_argv):
test()
