commit 3d70f7aef614c396f516b5fccedeebe98598714d
author Dong-hee Na <donghee.na92@gmail.com> Sat Jun 23 23:46:32 2018 +0900
committer Eric V. Smith <ericvsmith@users.noreply.github.com> Sat Jun 23 10:46:32 2018 -0400
tree b811dc51f5c680418baa0629eb16fb5b6fca9b94
parent 66ecefcfe77348ce12d3a951e8e6cd3ad274b24a

bpo-33805: Improve error message of dataclasses.replace() (GH-7580)

Lib/dataclasses.py

diff --git a/Lib/dataclasses.py b/Lib/dataclasses.py
index 96bf6e1..ad7bf0f 100644
--- a/Lib/dataclasses.py
+++ b/Lib/dataclasses.py
@@ -1173,6 +1173,9 @@
             continue
 
         if f.name not in changes:
+            if f._field_type is _FIELD_INITVAR:
+                raise ValueError(f"InitVar {f.name!r} "
+                                 'must be specified with replace()')
             changes[f.name] = getattr(obj, f.name)
 
     # Create the new object, which calls __init__() and