Make import tensorboard as tb possible

This change introduces a lazy loader that will allow us to provide some of the
conviences TensorFlow has. For example:

    import tensorboard as tb
    tb.summary.scalar('foo', tensor)

Only the hourglass summary module has been made available in this namespace,
since that's probably the only thing where we're 100% positive we want this
functionality.

tensorboard/BUILD

@@ -28,6 +28,17 @@ py_binary(
     ],
 )
 
+py_library(
+    name = "lib",
+    srcs = ["__init__.py"],
+    srcs_version = "PY2AND3",
+    visibility = ["//visibility:public"],
+    deps = [
+        ":lazy",
+        ":summary",
+    ],
+)
+
 py_library(
     name = "program",
     srcs = ["program.py"],
@@ -309,7 +320,7 @@ py_test(
     srcs = ["summary_test.py"],
     srcs_version = "PY2AND3",
     deps = [
-        ":summary",
+        ":lib",
         "//tensorboard:expect_tensorflow_installed",
     ],
 )
@@ -326,3 +337,9 @@ py_library(
         "//tensorboard:expect_tensorflow_installed",
     ],
 )
+
+py_library(
+    name = "lazy",
+    srcs = ["lazy.py"],
+    srcs_version = "PY2AND3",
+)

tensorboard/__init__.py

@@ -12,3 +12,20 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 # ==============================================================================
+"""TensorBoard is a webapp for understanding TensorFlow runs and graphs.
+"""
+
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+
+from tensorboard import lazy
+
+pkg = lambda i: i  # helps google sync process
+mod = lambda i: lazy.LazyLoader(i[i.rindex('.') + 1:], globals(), i)
+
+summary = mod(pkg('tensorboard.summary'))
+
+del lazy
+del mod
+del pkg

tensorboard/lazy.py

@@ -0,0 +1,54 @@
+# Copyright 2017 The TensorFlow Authors. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+# ==============================================================================
+"""TensorBoard is a webapp for understanding TensorFlow runs and graphs.
+"""
+
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+
+import importlib
+import types
+
+
+class LazyLoader(types.ModuleType):
+  """Lazily import a module, mainly to avoid pulling in large dependencies."""
+
+  # The lint error here is incorrect.
+  def __init__(self, local_name, parent_module_globals, name):  # pylint: disable=super-on-old-class
+    self._local_name = local_name
+    self._parent_module_globals = parent_module_globals
+
+    super(LazyLoader, self).__init__(name)
+
+  def _load(self):
+    # Import the target module and insert it into the parent's namespace
+    module = importlib.import_module(self.__name__)
+    self._parent_module_globals[self._local_name] = module
+
+    # Update this object's dict so that if someone keeps a reference to the
+    #   LazyLoader, lookups are efficient (__getattr__ is only called on lookups
+    #   that fail).
+    self.__dict__.update(module.__dict__)
+
+    return module
+
+  def __getattr__(self, item):
+    module = self._load()
+    return getattr(module, item)
+
+  def __dir__(self):
+    module = self._load()
+    return dir(module)

tensorboard/summary_test.py

@@ -18,14 +18,15 @@
 public entry point for end users, so we should be as careful as possible
 to ensure that we export the right things.
 """
+
 from __future__ import absolute_import
 from __future__ import division
 from __future__ import print_function
 
 import collections
 
+import tensorboard as tb
 import tensorflow as tf
-from tensorboard import summary
 
 
 STANDARD_PLUGINS = frozenset([
@@ -43,15 +44,15 @@ class SummaryExportsTest(tf.test.TestCase):
 
   def test_each_plugin_has_an_export(self):
     for plugin in STANDARD_PLUGINS:
-      self.assertIsInstance(getattr(summary, plugin), collections.Callable)
+      self.assertIsInstance(getattr(tb.summary, plugin), collections.Callable)
 
   def test_plugins_export_pb_functions(self):
     for plugin in STANDARD_PLUGINS:
       self.assertIsInstance(
-          getattr(summary, '%s_pb' % plugin), collections.Callable)
+          getattr(tb.summary, '%s_pb' % plugin), collections.Callable)
 
   def test_all_exports_correspond_to_plugins(self):
-    exports = [name for name in dir(summary) if not name.startswith('_')]
+    exports = [name for name in dir(tb.summary) if not name.startswith('_')]
     futures = frozenset(('absolute_import', 'division', 'print_function'))
     bad_exports = [
         name for name in exports