Load the `tf.contrib` module on demand only.

This change makes it so that `tf.contrib` and the libraries it
contains are not loaded until their first use. The rationale for this
change is that `tf.contrib` has a lower code quality than the other
`tf.*` libraries, and it frequently breaks users due to undeclared
dependencies or other churn.

See e.g. https://github.com/tensorflow/tensorflow/issues/2388 for an
example of where `import tensorflow as tf` fails due to a breakage in
`tf.contrib`. This issue
(https://github.com/tensorflow/tensorflow/issues/2154) shows a
dependency on a particular version of pandas.
Change: 131332657

1 files changed, 15 insertions, 0 deletions

diff --git a/tensorflow/__init__.py b/tensorflow/__init__.py
index 4fc5d8e816..ec7cd91e7e 100644
--- a/tensorflow/__init__.py
+++ b/tensorflow/__init__.py
@@ -21,3 +21,18 @@ from __future__ import division
 from __future__ import print_function
 
 from tensorflow.python import *
+
+
+# Lazily import the `tf.contrib` module. This avoids loading all of the
+# dependencies of `tf.contrib` at `import tensorflow` time.
+class _LazyContribLoader(object):
+
+  def __getattr__(self, item):
+    global contrib
+    # Replace the lazy loader with the imported module itself.
+    import importlib  # pylint: disable=g-import-not-at-top
+    contrib = importlib.import_module('tensorflow.contrib')
+    return getattr(contrib, item)
+
+
+contrib = _LazyContribLoader()