merged = tf.summary.merge_all()引起的出错：You must feed a value for placeholder tensor ‘input/y-input‘

在IPython环境下运行tensorflow1.15版本，运行以下代码会报错

import tensorflow as tf
import numpy as np

tf.reset_default_graph()
def add_layer(inputs, in_size, out_size, n_layer, activation_function=None):
    # add one more layer and return the output of this layer
    layer_name = 'layer%s' % n_layer
    with tf.name_scope(layer_name):
        with tf.name_scope('weights'):
            Weights = tf.Variable(tf.random_normal([in_size, out_size]), name='W')
            tf.summary.histogram(layer_name + '/weights', Weights)
        with tf.name_scope('biases'):
            biases = tf.Variable(tf.zeros([1, out_size]) + 0.1, name='b')
            tf.summary.histogram(layer_name + '/biases', biases)
        with tf.name_scope('Wx_plus_b'):
            Wx_plus_b = tf.add(tf.matmul(inputs, Weights), biases)
        if activation_function is None:
            outputs = Wx_plus_b
        else:
            outputs = activation_function(Wx_plus_b, )
        tf.summary.histogram(layer_name + '/outputs', outputs)
    return outputs


# Make up some real data
x_data = np.linspace(-1, 1, 300)[:, np.newaxis]
noise = np.random.normal(0, 0.05, x_data.shape)
y_data = np.square(x_data) - 0.5 + noise

# define placeholder for inputs to network
with tf.name_scope('inputs'):
    xs = tf.placeholder(tf.float32, [None, 1], name='x_input')
    ys = tf.placeholder(tf.float32, [None, 1], name='y_input')

# add hidden layer
l1 = add_layer(xs, 1, 10, n_layer=1, activation_function=tf.nn.relu)
# add output layer
prediction = add_layer(l1, 10, 1, n_layer=2, activation_function=None)

# the error between prediciton and real data
with tf.name_scope('loss'):
    loss = tf.reduce_mean(tf.reduce_sum(tf.square(ys - prediction),
                                        reduction_indices=[1]))
    tf.summary.scalar('loss', loss)

with tf.name_scope('train'):
    train_step = tf.train.GradientDescentOptimizer(0.1).minimize(loss)

sess = tf.Session()
merged = tf.summary.merge_all()

writer = tf.summary.FileWriter("logs/", sess.graph)

init = tf.global_variables_initializer()
sess.run(init)

for i in range(1000):
    sess.run(train_step, feed_dict={
    
    xs: x_data, ys: y_data})
    if i % 50 == 0:
        result = sess.run(merged,
                          feed_dict={
    
    xs: x_data, ys: y_data})
        writer.add_summary(result, i)

报错

raise type(e)(node_def, op, message) InvalidArgumentError: You must 
feed a value for placeholder tensor 'inputs/x_input' with dtype 
float and shape [?,1]

跟着莫烦的代码复制粘贴也能出错？查了一下午，莫烦用的是IDLE，我用的是基于IPython的spyder，而在IPython中，每次访问张量时，它都会上一次执行的基础生成新的张量，因此在调用tf.merge_all_summaries() 它最后返回的图可能会出现多个，如下图，原本打算画网络结构图，结果画出了3个除了名字其他一模一样的，甚至会出现如上所述的报错。
解决办法：
在每次在IPython环境下面运行tensorflow时，在最前面一行加入这样一行代码，亲测有效。

tf.reset_default_graph()

图1 重复的网络结构

参考文献

stackoverflow上各种解决方案
在这篇博客上找到解决办法
关于tf.reset_default_graph()函数的讲解