commit bbef7abe922edadc7a1679c19d6053240bf600d5
author Miss Islington (bot) <31488909+miss-islington@users.noreply.github.com> Sat Jun 23 08:04:01 2018 -0700
committer GitHub <noreply@github.com> Sat Jun 23 08:04:01 2018 -0700
tree 12ef3900638587c3aedab02dd2b6a0065bdf0d6d
parent efc6bf66a58e96c12116d65984ac69b0f36f85de

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

(cherry picked from commit 3d70f7aef614c396f516b5fccedeebe98598714d)

Co-authored-by: Dong-hee Na <donghee.na92@gmail.com>

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