test.py

import tensorflow as tf

q1 = tf.FIFOQueue(capacity=100, dtypes=[tf.int32], shapes=[[]])
q2 = tf.FIFOQueue(capacity=100, dtypes=[tf.int32], shapes=[[]])
q3 = tf.FIFOQueue(capacity=100, dtypes=[tf.int32], shapes=[[]])

idx = tf.placeholder(tf.int32)

def deq1():
    return tf.Print(q1.dequeue(), [1], "deq1 called")

def deq2():
    return tf.Print(q2.dequeue(), [2], "deq2 called")

def deq3():
    return tf.Print(q3.dequeue(), [3], "deq3 called")

batch = tf.cond(tf.equal(idx[0], 1), deq1, lambda: tf.cond(tf.equal(idx[0], 2), deq2, deq3))

s = tf.InteractiveSession()
s.run(tf.initialize_all_variables())
tf.train.start_queue_runners(sess=s)

for i in range(10):
    s.run(q1.enqueue(10+i))
    s.run(q2.enqueue(20+i))
    s.run(q3.enqueue(30+i))

print(s.run(batch, feed_dict={idx: [1]}))
print(s.run(batch, feed_dict={idx: [2]}))