Threaded tensorflow training on python 3

CHANGELOG.rst

@@ -20,6 +20,9 @@ Removed
 
 Fixed
 -----
+- Allow training of pipelines containing ``EmbeddingIntentClassifier`` in
+  a separate thread on python 3. This makes http server calls to ``/train``
+  non-blocking
 
 
 [0.13.5] - 2018-09-28

rasa_nlu/data_router.py

@@ -10,6 +10,7 @@
 from concurrent.futures import ProcessPoolExecutor as ProcessPool
 from typing import Text, Dict, Any, Optional, List
 
+import six
 from builtins import object
 from twisted.internet import reactor
 from twisted.internet.defer import Deferred
@@ -358,9 +359,9 @@ def training_errback(failure):
         self._current_training_processes += 1
         self.project_store[project].current_training_processes += 1
 
-        # tensorflow training is not executed in a separate thread, as this may
-        # cause training to freeze
-        if self._tf_in_pipeline(train_config):
+        # tensorflow training is not executed in a separate thread on python 2,
+        # as this may cause training to freeze
+        if six.PY2 and self._tf_in_pipeline(train_config):
             try:
                 logger.warning("Training a pipeline with a tensorflow "
                                "component. This blocks the server during "