How to determine placeholder dependency in TensorFlow

Question

Given a few symbolic variables to fetch, I need to know which placeholders are dependency.

In Theano, we have:

import theano as th
import theano.tens         


        

Answer 1

There's not an built-in function (that I know of), but it's easy to make one:

# Setup a graph
import tensorflow as tf
placeholder0 = tf.placeholder(tf.float32, [])
placeholder1 = tf.placeholder(tf.float32, [])
constant0 = tf.constant(2.0)
sum0 = tf.add(placeholder0, constant0)
sum1 = tf.add(placeholder1, sum0)

# Function to get *all* dependencies of a tensor.
def get_dependencies(tensor):
    dependencies = set()
    dependencies.update(tensor.op.inputs)
    for sub_op in tensor.op.inputs:
        dependencies.update(get_dependencies(sub_op))
    return dependencies

print(get_dependencies(sum0))
print(get_dependencies(sum1))
# Filter on type to get placeholders.
print([tensor for tensor in get_dependencies(sum0) if tensor.op.type == 'Placeholder'])
print([tensor for tensor in get_dependencies(sum1) if tensor.op.type == 'Placeholder'])

Of course, you could throw the placeholder filtering into the function as well.