Add missing SessionCreatorAdapter

examples/keras/README.md

@@ -38,5 +38,5 @@ Keras does not respect variable scopes or variable
 collections, which contradicts with tensorpack trainers.
 Therefore Keras support is __experimental__. 
 
-These simple examples can run within tensorpack smoothly, but note that a future version
-of Keras may break them (unlikely, though).
+These simple examples can run within tensorpack smoothly, but note that a future
+version of Keras or a complicated model may break them (unlikely, though).

tensorpack/tfutils/sesscreate.py

@@ -8,7 +8,7 @@ from ..tfutils.common import tfv1
 from ..utils import logger
 from .common import get_default_sess_config
 
-__all__ = ['NewSessionCreator', 'ReuseSessionCreator']
+__all__ = ['NewSessionCreator', 'ReuseSessionCreator', 'SessionCreatorAdapter']
 
 """
 A SessionCreator should:
@@ -49,6 +49,9 @@ bugs. See https://github.com/tensorpack/tensorpack/issues/497 for workarounds.")
 
 
 class ReuseSessionCreator(tfv1.train.SessionCreator):
+    """
+    Returns an existing session.
+    """
     def __init__(self, sess):
         """
         Args:
@@ -58,3 +61,22 @@ class ReuseSessionCreator(tfv1.train.SessionCreator):
 
     def create_session(self):
         return self.sess
+
+
+class SessionCreatorAdapter(tfv1.train.SessionCreator):
+    """
+    Apply a function on the output of a SessionCreator. Can be used to create a debug session.
+    """
+    def __init__(self, session_creator, func):
+        """
+        Args:
+            session_creator (tf.train.SessionCreator): a session creator
+            func (tf.Session -> tf.Session): takes a session created by
+            ``session_creator``, and return a new session to be returned by ``self.create_session``
+        """
+        self._creator = session_creator
+        self._func = func
+
+    def create_session(self):
+        sess = self._creator.create_session()
+        return self._func(sess)