Tensorflow FailedPreconditionError while trying to save frozen model - python-2.7

Question

I'm training a CNN with word embeddings and for some reason I'm getting FailedPreconditionError exception whenever I try to save a frozen version of the model for later use.
This is despite the fact that I call sess.run(tf.global_variables_initializer()) just before training and I have no problem training and checkpointing the model.
The problem occurs when I try to load a model from a checkpoint and save a frozen model. The function I'm using is as follows:
def freeze_model(checkpoint_path, model_save_path, output_node_names):
checkpoint = tf.train.get_checkpoint_state(checkpoint_path)
input_checkpoint = checkpoint.model_checkpoint_path
saver = tf.train.import_meta_graph(input_checkpoint + '.meta', clear_devices=True)
graph = tf.get_default_graph()
input_graph_def = graph.as_graph_def()
with tf.Session() as sess:
saver.restore(sess, input_checkpoint)
output_graph_def = graph_util.convert_variables_to_constants(
sess,
input_graph_def,
output_node_names
)
with tf.gfile.GFile(model_save_path, "wb") as f:
f.write(output_graph_def.SerializeToString())
The error I get is:
Traceback (most recent call last):
File "myproject/train.py", line 522, in <module>
tf.app.run()
File "/home/foo/anaconda2/lib/python2.7/site-packages/tensorflow/python/platform/app.py", line 44, in run
_sys.exit(main(_sys.argv[:1] + flags_passthrough))
File "myproject/train.py", line 518, in main
trainer.save_model(preprocessor)
File "myproject/train.py", line 312, in save_model
ut.freeze_model(self.checkpoint_dir, model_save_path, C.OUTPUT_NODE_NAMES)
File "/home/foo/anaconda2/lib/python2.7/site-packages/myproject/utils.py", line 224, in freeze_model
output_node_names
File "/home/foo/anaconda2/lib/python2.7/site-packages/tensorflow/python/framework/graph_util_impl.py", line 218, in convert_variables_to_constants
returned_variables = sess.run(variable_names)
File "/home/foo/anaconda2/lib/python2.7/site-packages/tensorflow/python/client/session.py", line 767, in run
run_metadata_ptr)
File "/home/foo/anaconda2/lib/python2.7/site-packages/tensorflow/python/client/session.py", line 965, in _run
feed_dict_string, options, run_metadata)
File "/home/foo/anaconda2/lib/python2.7/site-packages/tensorflow/python/client/session.py", line 1015, in _do_run
target_list, options, run_metadata)
File "/home/foo/anaconda2/lib/python2.7/site-packages/tensorflow/python/client/session.py", line 1035, in _do_call
raise type(e)(node_def, op, message)
tensorflow.python.framework.errors_impl.FailedPreconditionError: Attempting to use uninitialized value embeddings/W
[[Node: embeddings/W/_20 = _Send[T=DT_FLOAT, client_terminated=false, recv_device="/job:localhost/replica:0/task:0/cpu:0", send_device="/job:localhost/replica:0/task:0/gpu:0", send_device_incarnation=1, tensor_name="edge_30_embeddings/W", _device="/job:localhost/replica:0/task:0/gpu:0"](embeddings/W)]]
[[Node: conv_maxpool_4/W/_17 = _Recv[_start_time=0, client_terminated=false, recv_device="/job:localhost/replica:0/task:0/cpu:0", send_device="/job:localhost/replica:0/task:0/gpu:0", send_device_incarnation=1, tensor_name="edge_26_conv_maxpool_4/W", tensor_type=DT_FLOAT, _device="/job:localhost/replica:0/task:0/cpu:0"]()]]

Answer 1

Turns out I was constructing a Saver object before I made a Session so nothing from the session was being saved.