Refactor the python system_impl module.

mojo/PRESUBMIT.py

Index: mojo/PRESUBMIT.py
diff --git a/mojo/PRESUBMIT.py b/mojo/PRESUBMIT.py
index 3d85422260f36eaa0dedbc8672ff20417c7836be..32273671444c1f547def158270caacc9254798e3 100644
--- a/mojo/PRESUBMIT.py
+++ b/mojo/PRESUBMIT.py
@@ -20,8 +20,9 @@ _SDK_WHITELISTED_EXTERNAL_PATHS = [
 _PACKAGE_PATH_PREFIXES = {"SDK": "mojo/public/",
                           "EDK": "mojo/edk/"}
 
-_PACKAGE_SOURCE_SET_TYPES = {"SDK": "mojo_sdk_source_set",
-                             "EDK": "mojo_edk_source_set"}
+_PACKAGE_SOURCE_SET_TYPES = {"SDK": ["mojo_sdk_source_set",
+                                     "python_binary_source_set"],
+                             "EDK": ["mojo_edk_source_set"]}
 
 _ILLEGAL_EXTERNAL_PATH_WARNING_MESSAGE = \
     "Found disallowed external paths within SDK buildfiles."
@@ -161,7 +162,7 @@ def _CheckSourceSetsAreOfCorrectType(input_api, output_api, package):
       if not m:
         continue
       source_set_type = m.group(0)[:-1]
-      if source_set_type == required_source_set_type:
+      if source_set_type in required_source_set_type:
         continue
       problems.append(_IncorrectSourceSetTypeWarningItem(f.LocalPath(),
                                                          line_num))