bpo-38431: fix dataclasses.InitVar.__repr__

Fix repr method of InitVar to work with typing objects.

Author: samuelcolvin

Lib/dataclasses.py

@@ -206,7 +206,12 @@ def __init__(self, type):
         self.type = type
 
     def __repr__(self):
-        return f'dataclasses.InitVar[{self.type.__name__}]'
+        try:
+            type_name = self.type.__name__
+        except AttributeError:
+            # typing objects, e.g. Union
+            type_name = repr(self.type)
+        return f'dataclasses.InitVar[{type_name}]'
 
     def __class_getitem__(cls, type):
         return InitVar(type)

Lib/test/test_dataclasses.py

@@ -2883,6 +2883,11 @@ class C:
                 # x is not an InitVar, so there will be a member x.
                 self.assertEqual(C(10).x, 10)
 
+    def test_initvar_repr(self):
+        self.assertEqual(repr(InitVar[str]), 'dataclasses.InitVar[str]')
+        self.assertEqual(repr(InitVar[Optional[str]]),
+                         'dataclasses.InitVar[typing.Union[str, NoneType]]')
+
     def test_classvar_module_level_import(self):
         from test import dataclass_module_1
         from test import dataclass_module_1_str

Misc/ACKS

@@ -321,6 +321,7 @@ Benjamin Collar
 Jeffery Collins
 Robert Collins
 Paul Colomiets
+Samuel Colvin
 Christophe Combelles
 Geremy Condra
 Denver Coneybeare

Misc/NEWS.d/next/Library/2019-10-10-16-53-00.bpo-38431.d5wzNp.rst

@@ -0,0 +1 @@
+Fix ``__repr__`` method for :class:`dataclasses.InitVar` to support typing objects.