Properly mock ray submodules when building documentation. (#337)

doc/source/conf.py

@@ -16,6 +16,12 @@ import sys
 import os
 import shlex
 
+# These lines added to enable Sphinx to work without installing Ray.
+import mock
+MOCK_MODULES = ["ray.numbuf", "ray.local_scheduler", "ray.plasma"]
+for mod_name in MOCK_MODULES:
+  sys.modules[mod_name] = mock.Mock()
+
 # If extensions (or modules to document with autodoc) are in another directory,
 # add these directories to sys.path here. If the directory is relative to the
 # documentation root, use os.path.abspath to make it absolute, like shown here.