TensorFlow 复制placeholder

用这种方式复制placeholder：

= tf.placeholder(tf.int32, 
  [batch_size, sequence_len], 
  name="input")

copy_input = tf.Variable(initial_value=input_placeholder, 
  trainable=False)

然后这句报错：you must feed a value for placeholder tensor

sess.run(tf.global_variables_initializer())

解决方案：
用这种方式复制placeholder：

copy_input = tf.get_variable(
                initializer=tf.constant(0, shape=[batch_size, sequence_len]),    
                name="copy_placeholder",
                dtype=tf.int32, trainable=False)
copy_input.assign(input_placeholder)