Tf.Print（）不打印张量的形状吗？

Question

我使用Tensorflow编写了一个简单的分类程序，并获得了输出，除了我尝试打印用于模型参数，特征和偏差的张量的形状。功能定义：

import tensorflow as tf, numpy as np
from tensorflow.examples.tutorials.mnist import input_data


def get_weights(n_features, n_labels):
#    Return weights
    return tf.Variable( tf.truncated_normal((n_features, n_labels)) )

def get_biases(n_labels):
    # Return biases
    return tf.Variable( tf.zeros(n_labels))

def linear(input, w, b):
    #  Linear Function (xW + b)
#     return np.dot(input,w) + b 
    return tf.add(tf.matmul(input,w), b)

def mnist_features_labels(n_labels):
    """Gets the first <n> labels from the MNIST dataset
    """
    mnist_features = []
    mnist_labels = []
    mnist = input_data.read_data_sets('dataset/mnist', one_hot=True)

    # In order to make quizzes run faster, we're only looking at 10000 images
    for mnist_feature, mnist_label in zip(*mnist.train.next_batch(10000)):

        # Add features and labels if it's for the first <n>th labels
        if mnist_label[:n_labels].any():
            mnist_features.append(mnist_feature)
            mnist_labels.append(mnist_label[:n_labels])

    return mnist_features, mnist_labels

图形创建：

# Number of features (28*28 image is 784 features)
n_features = 784
# Number of labels
n_labels = 3

# Features and Labels
features = tf.placeholder(tf.float32)
labels = tf.placeholder(tf.float32)

# Weights and Biases
w = get_weights(n_features, n_labels)
b = get_biases(n_labels)

# Linear Function xW + b
logits = linear(features, w, b)

# Training data
train_features, train_labels = mnist_features_labels(n_labels)

print("Total {0} data points of Training Data, each having {1} features \n \
      Total {2} number of labels,each having 1-hot encoding {3}".format(len(train_features),len(train_features[0]),\
                                                                     len(train_labels),train_labels[0]
                                                                      )
     )

# global variables initialiser
init= tf.global_variables_initializer()

with tf.Session() as session:

    session.run(init)

问题在这里：

#            shapes =tf.Print ( tf.shape(features), [tf.shape(features),
#                                                     tf.shape(labels),
#                                                     tf.shape(w),
#                                                     tf.shape(b),
#                                                     tf.shape(logits)
#                                                     ], message= "The shapes are:" )
#         print("Verify shapes",shapes)
    logits = tf.Print(logits, [tf.shape(features),
                           tf.shape(labels),
                           tf.shape(w),
                           tf.shape(b),
                           tf.shape(logits)],
                  message= "The shapes are:")
    print(logits)

我在这里看了看，但发现没有什么用。

    # Softmax
    prediction = tf.nn.softmax(logits)

    # Cross entropy
    # This quantifies how far off the predictions were.
    # You'll learn more about this in future lessons.
    cross_entropy = -tf.reduce_sum(labels * tf.log(prediction), reduction_indices=1)

    # Training loss
    # You'll learn more about this in future lessons.
    loss = tf.reduce_mean(cross_entropy)

    # Rate at which the weights are changed
    # You'll learn more about this in future lessons.
    learning_rate = 0.08

    # Gradient Descent
    # This is the method used to train the model
    # You'll learn more about this in future lessons.
    optimizer = tf.train.GradientDescentOptimizer(learning_rate).minimize(loss)

    # Run optimizer and get loss
    _, l = session.run(
        [optimizer, loss],
        feed_dict={features: train_features, labels: train_labels})

# Print loss
print('Loss: {}'.format(l))

我得到的输出是：

Extracting dataset/mnist/train-images-idx3-ubyte.gz
Extracting dataset/mnist/train-labels-idx1-ubyte.gz
Extracting dataset/mnist/t10k-images-idx3-ubyte.gz
Extracting dataset/mnist/t10k-labels-idx1-ubyte.gz
Total 3118 data points of Training Data, each having 784 features 
       Total 3118 number of labels,each having 1-hot encoding [0. 1. 0.]
Tensor("Print_22:0", shape=(?, 3), dtype=float32)
Loss: 5.339271068572998

谁能帮助我理解为什么我看不到张量的形状？

Answer 1

那不是你的用法tf.Print。它是一个操作，它本身不执行任何操作（仅返回输入），但会打印请求的张量作为副作用。你应该做类似的事情

logits = tf.Print(logits, [tf.shape(features),
                           tf.shape(labels),
                           tf.shape(w),
                           tf.shape(b),
                           tf.shape(logits)],
                  message= "The shapes are:")

现在，无论何时logits进行评估（将用于计算损耗/梯度），都将打印形状信息。

您现在正在做的只是打印tf.Printop 的返回值，即它的输入（tf.shape(features)）。