bpo-38431: Fix __repr__ method of InitVar to work with typing objects. (GH-16702)

(cherry picked from commit 793cb85)

Co-authored-by: Samuel Colvin <samcolvin@gmail.com>

Author: miss-islington

Lib/dataclasses.py

@@ -210,7 +210,12 @@ def __init__(self, type):
         self.type = type
 
     def __repr__(self):
-        return f'dataclasses.InitVar[{self.type.__name__}]'
+        if isinstance(self.type, type):
+            type_name = self.type.__name__
+        else:
+            # typing objects, e.g. List[int]
+            type_name = repr(self.type)
+        return f'dataclasses.InitVar[{type_name}]'
 
 
 # Instances of Field are only ever created from within this module,

Lib/test/test_dataclasses.py

@@ -1102,6 +1102,8 @@ def test_init_var_preserve_type(self):
 
         # Make sure the repr is correct.
         self.assertEqual(repr(InitVar[int]), 'dataclasses.InitVar[int]')
+        self.assertEqual(repr(InitVar[List[int]]),
+                         'dataclasses.InitVar[typing.List[int]]')
 
     def test_init_var_inheritance(self):
         # Note that this deliberately tests that a dataclass need not

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, patch by Samuel Colvin.