Add exception inference for UnicodeDecodeError (#797)

Close pylint-dev/pylint#3639

ChangeLog

@@ -15,6 +15,10 @@ Release Date: TBA
 
 * Added more supported parameters to ``subprocess.check_output``
 
+* Added exception inference for `UnicodeDecodeError`
+
+  Close PyCQA/pylint#3639
+
 
 What's New in astroid 2.4.2?
 ============================

astroid/interpreter/objectmodel.py

@@ -659,9 +659,16 @@ def attr_path(self):
         return node_classes.Const("")
 
 
+class UnicodeDecodeErrorInstanceModel(ExceptionInstanceModel):
+    @property
+    def attr_object(self):
+        return node_classes.Const("")
+
+
 BUILTIN_EXCEPTIONS = {
     "builtins.SyntaxError": SyntaxErrorInstanceModel,
     "builtins.ImportError": ImportErrorInstanceModel,
+    "builtins.UnicodeDecodeError": UnicodeDecodeErrorInstanceModel,
     # These are all similar to OSError in terms of attributes
     "builtins.OSError": OSErrorInstanceModel,
     "builtins.BlockingIOError": OSErrorInstanceModel,

tests/unittest_object_model.py

@@ -586,6 +586,17 @@ def test_oserror(self):
             assert isinstance(inferred, astroid.Const)
             assert inferred.value == value
 
+    def test_unicodedecodeerror(self):
+        code = """
+        try:
+            raise UnicodeDecodeError("utf-8", "blob", 0, 1, "reason")
+        except UnicodeDecodeError as error:
+            error.object[:1] #@
+        """
+        node = builder.extract_node(code)
+        inferred = next(node.infer())
+        assert isinstance(inferred, astroid.Const)
+
     def test_import_error(self):
         ast_nodes = builder.extract_node(
             """