message: import contextmanager in side_effect_guards.py
diff: @@ -34,6 +34,8 @@ from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  +from contextlib import contextmanager
  +
  import gast
  from tensorflow.contrib.py2tf.pyct import anno
  @@ -123,7 +125,7 @@ class SideEffectGuardTransformer(gast.NodeTransformer):
  temp_result = (temp_result,)
  ctx = tf.control_dependencies(temp_result) # pylint:disable=undefined-variable
  else:
  - ctx = contextmanager(lambda: (yield))() # pylint:disable=undefined-variable
  + ctx = contextmanager(lambda: (yield))()
  with ctx:
  # TODO(mdan): Also insert ops to re-fetch if variables are involved.
  pass # Will be removed below.
  