1 files changed, 20 insertions, 3 deletions
diff --git a/python/m5/smartdict.py b/python/m5/smartdict.py
index e282bc07b..4ea8210d3 100644
--- a/python/m5/smartdict.py
+++ b/python/m5/smartdict.py
@@ -1,6 +1,23 @@
+# The SmartDict class fixes a couple of issues with using the content
+# of os.environ or similar dicts of strings as Python variables:
+#
+# 1) Undefined variables should return False rather than raising KeyError.
+#
+# 2) String values of 'False', '0', etc., should evaluate to False
+#    (not just the empty string).
+#
+# #1 is solved by overriding __getitem__, and #2 is solved by using a
+# proxy class for values and overriding __nonzero__ on the proxy.
+# Everything else is just to (a) make proxies behave like normal
+# values otherwise, (b) make sure any dict operation returns a proxy
+# rather than a normal value, and (c) coerce values written to the
+# dict to be strings.
+
+
 from convert import *
 
 class SmartDict(dict):
+
     class Proxy(str):
         def __int__(self):
             return int(to_integer(str(self)))
@@ -58,7 +75,7 @@ class SmartDict(dict):
 
 
     def __getitem__(self, key):
-        return self.Proxy(dict.__getitem__(self, key))
+        return self.Proxy(dict.get(self, key, 'False'))
 
     def __setitem__(self, key, item):
         dict.__setitem__(self, key, str(item))
@@ -77,9 +94,9 @@ class SmartDict(dict):
         for key,value in dict.iteritems(self):
             yield key, self.Proxy(value)
 
-    def get(self, key, default=''):
+    def get(self, key, default='False'):
         return self.Proxy(dict.get(self, key, str(default)))
 
-    def setdefault(self, key, default=''):
+    def setdefault(self, key, default='False'):
         return self.Proxy(dict.setdefault(self, key, str(default)))