Clean up BUILD_simulator.py

tools/BUILD_simulator.py

 #!/usr/bin/env python
 #
 # Copyright 2015 Google Inc.
 #
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # This script does a very rough simulation of BUILD file expansion,
 # mostly to see the effects of glob().
 
 # We start by adding some symbols to our namespace that BUILD.public calls.
 
-# We don't really care about this, so just no-op it.
-def exports_files(files):
+import glob
+import pprint
+
+def noop(*args, **kwargs):
   pass
 
 # Simulates BUILD file glob().
-def glob(include, exclude=()):
-  from glob import glob as python_glob
-
+def BUILD_glob(include, exclude=()):
   files = set()
   for pattern in include:
-    files.update(python_glob(pattern))
+    files.update(glob.glob(pattern))
   for pattern in exclude:
-    files.difference_update(python_glob(pattern))
+    files.difference_update(glob.glob(pattern))
   return list(sorted(files))
 
-# We've put enough into our environment now to treat BUILD.public as if it were
-# Python code.  This pulls its variable definitions (SRCS, HDRS, DEFINES, etc.)
-# into our local namespace.
-execfile('BUILD.public')
+# With these namespaces, we can treat BUILD.public as if it were
+# Python code.  This pulls its variable definitions (SRCS, HDRS,
+# DEFINES, etc.) into local_names.
+global_names = {
+  'exports_files': noop,
+  'glob': BUILD_glob,
+}
+local_names = {}
+execfile('BUILD.public', global_names, local_names)
 
-# Pretty-print every variable whose name is COMPLETELY_UPPERCASE,
-# i.e. every variable from BUILD.public.  This is obviously quite heuristic.
-from pprint import pprint
 with open('tools/BUILD.public.expected', 'w') as out:
   print >>out, "This file is auto-generated by tools/BUILD_simulator.py."
   print >>out, "It expands BUILD.public to make it easy to see changes."
-  for name, value in sorted(locals().items()):
-    if name.isupper():
-      print >>out, name, '= ',
-      pprint(value, out)
+  for name, value in sorted(local_names.items()):
+    print >>out, name, '= ',
+    pprint.pprint(value, out)