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, 27 insertions, 0 deletions

diff --git a/astroid/interpreter/objectmodel.py b/astroid/interpreter/objectmodel.py
index 7c32e6fc..af1205cd 100644
--- a/astroid/interpreter/objectmodel.py
+++ b/astroid/interpreter/objectmodel.py
@@ -41,6 +41,7 @@ mechanism.
 import itertools
 import pprint
 import os
+import types
 
 import six
 
@@ -518,3 +519,29 @@ class InstanceModel(ObjectModel):
     @property
     def py__dict__(self):
         return _dunder_dict(self._instance, self._instance.instance_attrs)
+
+
+class ExceptionInstanceModel(InstanceModel):
+
+    @property
+    def pyargs(self):
+        message = node_classes.Const('')
+        args = node_classes.Tuple(parent=self._instance)
+        args.postinit((message, ))
+        return args
+
+    if six.PY3:
+        # It's available only on Python 3.
+
+        @property
+        def py__traceback__(self):
+            builtins = astroid.MANAGER.builtins()
+            traceback_type = builtins[types.TracebackType.__name__]
+            return traceback_type.instantiate_class()
+
+    if six.PY2:
+        # It's available only on Python 2.
+
+        @property
+        def pymessage(self):
+            return node_classes.Const('')