--- a/configuration/configuration.py	Sun Mar 30 19:28:09 2014 -0700
+++ b/configuration/configuration.py	Sun Mar 30 19:53:20 2014 -0700
@@ -170,21 +170,18 @@
             if not flags:
                 args = ['--no-%s' % name]
             if not help:
-                kw['help'] = 'disable %s' % name
+                kw['help'] = 'disable {}'.format(name)
         else:
             kw['action'] = 'store_true'
             if not help:
-                kw['help'] = 'enable %s' % name
+                kw['help'] = 'enable {}'.format(name)
         return args, kw
 
+
 class ListCLI(BaseCLI):
 
     def __call__(self, name, value):
         args, kw = BaseCLI.__call__(self, name, value)
-
-        # TODO: could use 'extend'
-        # - http://hg.mozilla.org/build/mozharness/file/5f44ba08f4be/mozharness/base/config.py#l41
-
         kw['action'] = 'append'
         return args, kw
 
@@ -221,6 +218,7 @@
             raise AssertionError("Each value must be delimited by '%s': %s" % (self.delimeter, value))
         return value.split(self.delimeter, 1)
 
+# types of CLI arguments
 types = {bool:  BoolCLI(),
          int:   IntCLI(),
          float: FloatCLI(),
@@ -231,6 +229,7 @@
 
 __all__ += [i.__class__.__name__ for i in types.values()]
 
+
 class Configuration(optparse.OptionParser):
     """declarative configuration object"""
 
@@ -251,11 +250,10 @@
         # sanity check
         if isinstance(self.options, dict):
             self.option_dict = self.options
-        elif isinstance(self.options, list):
-            # XXX could also be tuple, etc
+        elif isinstance(self.options, (list, tuple)):
             self.option_dict = dict(self.options)
         else:
-            raise NotImplementedError
+            raise NotImplementedError("Configuration: `options` should be castable to a dict")
 
         # setup configuration
         self.config = {}
@@ -296,10 +294,12 @@
                                           help="Output configuration file; Formats: %s" % formats))
 
 
-    ### methods for iteration
-    ### TODO: make the class a real iterator
+    ### iteration
 
     def items(self):
+        """items in options"""
+        # TODO: make the class a real iterator
+
         # allow options to be a list of 2-tuples
         if isinstance(self.options, dict):
             return self.options.items()
@@ -315,7 +315,7 @@
         # ensure options in configuration are in self.options
         unknown_options = [i for i in config if i not in self.option_dict]
         if unknown_options:
-            raise UnknownOptionException("Unknown options: %s" % ', '.join(unknown_options))
+            raise UnknownOptionException("Unknown options: {}".format(', '.join(unknown_options)))
 
         # ensure options are of the right type (if specified)
         for key, value in config.items():
@@ -334,7 +334,7 @@
                     try:
                         config[key] = _type(value)
                     except BaseException, e:
-                        raise TypeCastException("Could not coerce %s, %s, to type %s: %s" % (key, value, _type.__name__, e))
+                        raise TypeCastException("Could not coerce '%s'=%s, to type %s: %s" % (key, value, _type.__name__, e))
 
         return config
 
@@ -348,11 +348,11 @@
                     if isinstance(required, basestring):
                         required_message = required
                     else:
-                        required_message = "Parameter %s is required but not present" % key
+                        required_message = "Parameter {} is required but not present".format(key)
                     # TODO: this should probably raise all missing values vs
                     # one by one
                     raise MissingValueException(required_message)
-        # TODO: configuration should be locked after this is called
+
 
     ### methods for adding configuration
 
@@ -372,7 +372,6 @@
 
     def __call__(self, *args):
         """add items to configuration and check it"""
-        # TODO: configuration should be locked after this is called
 
         # start with defaults
         self.config = self.default_config()
@@ -428,7 +427,7 @@
         if 'default' in value:
             default = value['default']
             if default is None:
-                return None
+                return None  # not <type 'NoneType'>
             return type(value['default'])
 
     def optparse_options(self, parser):
@@ -520,6 +519,7 @@
             # TODO: have a way of specifying format other than filename
             self.serialize(dump)
 
+
     ### serialization/deserialization
 
     def formats(self):