Merge pull request #577 from brianwa84/r0.8

R0.8 cherry-picks

README.md

@@ -34,10 +34,10 @@ __Layer 1: Statistical Building Blocks__
 
 __Layer 2: Model Building__
 
-* Edward2 ([`tfp.edward2`](https://github.com/tensorflow/probability/tree/master/tensorflow_probability/python/edward2)):
+* Edward2 ([`tfp.edward2`](https://github.com/tensorflow/probability/tree/master/tensorflow_probability/python/experimental/edward2)):
   A probabilistic programming language for specifying flexible probabilistic
   models as programs. See the
-  [Edward2 `README.md`](https://github.com/tensorflow/probability/tree/master/tensorflow_probability/python/edward2/README.md).
+  [Edward2 `README.md`](https://github.com/tensorflow/probability/blob/master/tensorflow_probability/python/experimental/edward2/README.md).
 * Probabilistic Layers ([`tfp.layers`](https://github.com/tensorflow/probability/tree/master/tensorflow_probability/python/layers)):
   Neural network layers with uncertainty over the functions they represent,
   extending TensorFlow Layers.

setup.py

@@ -32,6 +32,7 @@
     'numpy >= 1.13.3',
     'decorator',
     'cloudpickle == 1.1.1',
+    'gast >= 0.2, < 0.3'  # For autobatching
 ]
 
 if '--release' in sys.argv:

tensorflow_probability/python/__init__.py

@@ -21,23 +21,28 @@
 from tensorflow_probability.python import bijectors
 from tensorflow_probability.python import debugging
 from tensorflow_probability.python import distributions
-from tensorflow_probability.python import edward2
 from tensorflow_probability.python import experimental
 from tensorflow_probability.python import glm
 from tensorflow_probability.python import layers
 from tensorflow_probability.python import math
 from tensorflow_probability.python import mcmc
 from tensorflow_probability.python import monte_carlo
 from tensorflow_probability.python import optimizer
-from tensorflow_probability.python import positive_semidefinite_kernels
 from tensorflow_probability.python import stats
 from tensorflow_probability.python import sts
 from tensorflow_probability.python import trainable_distributions
 from tensorflow_probability.python import util
 from tensorflow_probability.python import vi
 
+from tensorflow.python.util import lazy_loader  # pylint: disable=g-direct-tensorflow-import
 from tensorflow.python.util.all_util import remove_undocumented  # pylint: disable=g-direct-tensorflow-import
 
+edward2 = lazy_loader.LazyLoader('edward2', globals(),
+                                 'tensorflow_probability.python.edward2')
+positive_semidefinite_kernels = lazy_loader.LazyLoader(
+    'positive_semidefinite_kernels', globals(),
+    'tensorflow_probability.python.positive_semidefinite_kernels')
+
 _allowed_symbols = [
     'bijectors',
     'debugging',