在tensorflow程序运行的时候一定要记住初始化

init=tf.global_variables_initializer()

with tf.Session() as sess

　　sess.run(init)

如果欠缺这一步会出现错误：

FailedPreconditionError                   Traceback (most recent call last)
~/anaconda3/lib/python3.6/site-packages/tensorflow/python/client/session.py in _do_call(self, fn, *args)
   1355     try:
-> 1356       return fn(*args)
   1357     except errors.OpError as e:

~/anaconda3/lib/python3.6/site-packages/tensorflow/python/client/session.py in _run_fn(feed_dict, fetch_list, target_list, options, run_metadata)
   1340       return self._call_tf_sessionrun(
-> 1341           options, feed_dict, fetch_list, target_list, run_metadata)
   1342 

~/anaconda3/lib/python3.6/site-packages/tensorflow/python/client/session.py in _call_tf_sessionrun(self, options, feed_dict, fetch_list, target_list, run_metadata)
   1428         self._session, options, feed_dict, fetch_list, target_list,
-> 1429         run_metadata)
   1430