张量流中的if语句（无其他）

Question

I want to have an if statement in tensorflow; and if the condition is not fulfilled nothing should happen.

I tried to use both tf.case and tf.cond but both require a specification of a function it the statement evaluates False.

op = tf.cond(tf.equal(x, y), true_fn=f1(), false_fn=lambda: None)

gives me an error: ValueError: false_fn must have a return value.

Answer 1

On TF 1.x, I would use tf.no_op to specify a dummy OP that does nothing:

ops = tf.cond(tf.equal(x, y), true_fn=f, false_fn=lambda: tf.no_op()) 

On TF 2.x, you can just pass lambda: None to false_fn , thanks to eager execution.

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Minimal Code Sample

import tensorflow as tf

x, y, z = tf.constant(1), tf.constant(1), tf.constant(2)
op1 = tf.cond(
    tf.equal(x, y), true_fn=lambda: tf.print(x), false_fn=lambda: tf.no_op())
op2 = tf.cond(
    tf.equal(x, z), true_fn=lambda: tf.print(x), false_fn=lambda: tf.no_op())

with tf.Session() as sess:
    sess.run(op1)  # 1
    sess.run(op2)  # does nothing

Answer 2

You can use tf.identy(tf)

namely

op = tf.cond(tf.equal(x, y), true_fn=f1(), false_fn=tf.identy(tf))

@see https://www.tensorflow.org/api_docs/python/tf/identity