Issue feeding a list into feed_dict in TensorFlow
feed_dict can be provided by preparing a dictionary beforehand as follows
n = 10
input_1 = [tf.placeholder(...) for _ in range(n)]
input_2 = tf.placeholder(...)
data_1 = [np.array(...) for _ in range(n)]
data_2 = np.array(...)
feed_dictionary = {}
for i in range(n):
feed_dictionary[input_1[i]] = data_1[i]
feed_dictionary[input_2] = data_2
sess.run(y, feed_dict=feed_dictionary)
Here is a correct example:
batch_size, input_size, n = 2, 3, 2
# in your case n = 10
x = tf.placeholder(tf.types.float32, shape=(n, batch_size, input_size))
y = tf.add(x, x)
data = np.random.rand(n, batch_size, input_size)
sess = tf.Session()
print sess.run(y, feed_dict={x: data})
And here is a strange things I see in your approach. For some reason you use 10 * [tf.placeholder(...)]
, which creates 10 tensors of size (batch_size, input_size)
. No idea why do you do this, if you can just create on Tensor of rank 3 (where the first dimension is 10).
Because you have a list of tensors (and not a tensor), you can not feed your data to this list (but in my case I can feed to my tensor).
There are two issues that are causing problems here:
The first issue is that the Session.run()
call only accepts a small number of types as the keys of the feed_dict
. In particular, lists of tensors are not supported as keys, so you have to put each tensor as a separate key.* One convenient way to do this is using a dictionary comprehension:
inputs = [tf.placeholder(...), ...]
data = [np.array(...), ...]
sess.run(y, feed_dict={i: d for i, d in zip(inputs, data)})
The second issue is that the 10 * [tf.placeholder(...)]
syntax in Python creates a list with ten elements, where each element is the same tensor object (i.e. has the same name
property, the same id
property, and is reference-identical if you compare two elements from the list using inputs[i] is inputs[j]
). This explains why, when you tried to create a dictionary using the list elements as keys, you ended up with a dictionary with a single element - because all of the list elements were identical.
To create 10 different placeholder tensors, as you intended, you should instead do the following:
inputs = [tf.placeholder(tf.float32, shape=(batch_size, input_size))
for _ in xrange(10)]
If you print the elements of this list, you'll see that each element is a tensor with a different name.
EDIT: * You can now pass tuples as the keys of a feed_dict
, because these may be used as dictionary keys.