Exceptions have their own object model

Some of exceptions's attributes, such as .args and .message,
can't be inferred correctly since they are descriptors that get
transformed into the proper objects at runtime. This can cause issues
with the static analysis, since they are inferred as different than
what's expected. Now when we're creating instances of exceptions,
we're inferring a special object that knows how to transform those
runtime attributes into the proper objects via a custom object model.
Closes #81

1 files changed, 12 insertions, 0 deletions

diff --git a/astroid/interpreter/objects.py b/astroid/interpreter/objects.py
index 3c61aef4..237caad6 100644
--- a/astroid/interpreter/objects.py
+++ b/astroid/interpreter/objects.py
@@ -277,6 +277,18 @@ class Instance(BaseInstance):
                 node=self, index=index, context=context))
 
 
+@util.register_implementation(runtimeabc.ExceptionInstance)
+class ExceptionInstance(Instance):
+    """Class for instances of exceptions
+
+    It has special treatment for some of the exceptions's attributes,
+    which are transformed at runtime into certain concrete objects, such as
+    the case of .args.
+    """
+
+    special_attributes = util.lazy_descriptor(lambda: objectmodel.ExceptionInstanceModel())
+
+
 class Method(Proxy):
 
     def __repr__(self):