Remember that some values are not fetchable

github/GithubObject.UnitTest.py

@@ -41,6 +41,8 @@ class GithubObjectWithOnlySimpleAttributes( TestCaseWithGithubTestObject ):
         self.assertEqual( self.o.a1, 1 )
         # - acknowledges updates of attributes
         self.assertEqual( self.o.a2, 22 )
+        # - remembers that some attributes are absent even after an update
+        self.assertEqual( self.o.a4, None )
 
     def testUnknownAttribute( self ):
         # A GithubObject:

github/GithubObject.py

@@ -3,18 +3,26 @@ class BadGithubObjectException( Exception ):
 
 class SimpleScalarAttributes:
     class AttributeDefinition:
+        def __init__( self, attributeNames ):
+            self.__attributeNames = attributeNames
+
         def getValueFromRawValue( self, obj, rawValue ):
             return rawValue
 
         def fetchRawValues( self, obj ):
-            return obj._github.rawRequest( "GET", "/test" )
+            attributes = obj._github.rawRequest( "GET", "/test" )
+            for attributeName in self.__attributeNames:
+                if attributeName not in attributes:
+                    attributes[ attributeName ] = None
+            return attributes
 
     def __init__( self, *attributeNames ):
         self.__attributeNames = attributeNames
 
     def getAttributeDefinitions( self ):
+        commonDefinition = SimpleScalarAttributes.AttributeDefinition( self.__attributeNames )
         return [
-            ( attributeName, SimpleScalarAttributes.AttributeDefinition() )
+            ( attributeName, commonDefinition )
             for attributeName in self.__attributeNames
         ]
 
@@ -44,7 +52,11 @@ def GithubObject( className, *attributePolicies ):
         def __updateAttributes( self, attributes ):
             for attributeName, attributeValue in attributes.iteritems():
                 attributeDefinition = attributeDefinitions[ attributeName ]
-                self.__attributes[ attributeName ] = attributeDefinition.getValueFromRawValue( self, attributeValue )
+                if attributeValue is None:
+                    if attributeName not in self.__attributes:
+                        self.__attributes[ attributeName ] = None
+                else:
+                    self.__attributes[ attributeName ] = attributeDefinition.getValueFromRawValue( self, attributeValue )
 
         def __fetchAttribute( self, attributeName ):
             attributeDefinition = attributeDefinitions[ attributeName ]