From 2b458c1dba4058c808fde25226bb2d91c5a909ca Mon Sep 17 00:00:00 2001
From: Ken Jin <28750310+Fidget-Spinner@users.noreply.github.com>
Date: Wed, 12 May 2021 21:47:11 +0800
Subject: [PATCH] bpo-44089: Allow subclassing of ``csv.Error`` (GH-26008)

* fix subclass error

* Update 2021-05-09-22-52-34.bpo-44089.IoANsN.rst
---
 Lib/test/test_csv.py                                           | 3 +++
 .../next/Library/2021-05-09-22-52-34.bpo-44089.IoANsN.rst      | 2 ++
 Modules/_csv.c                                                 | 2 +-
 3 files changed, 6 insertions(+), 1 deletion(-)
 create mode 100644 Misc/NEWS.d/next/Library/2021-05-09-22-52-34.bpo-44089.IoANsN.rst

diff --git a/Lib/test/test_csv.py b/Lib/test/test_csv.py
index 2411a91110d..a1e050acd2a 100644
--- a/Lib/test/test_csv.py
+++ b/Lib/test/test_csv.py
@@ -1237,6 +1237,9 @@ class MiscTestCase(unittest.TestCase):
         extra = {'__doc__', '__version__'}
         support.check__all__(self, csv, ('csv', '_csv'), extra=extra)
 
+    def test_subclassable(self):
+        # issue 44089
+        class Foo(csv.Error): ...
 
 if __name__ == '__main__':
     unittest.main()
diff --git a/Misc/NEWS.d/next/Library/2021-05-09-22-52-34.bpo-44089.IoANsN.rst b/Misc/NEWS.d/next/Library/2021-05-09-22-52-34.bpo-44089.IoANsN.rst
new file mode 100644
index 00000000000..b9bd963582f
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2021-05-09-22-52-34.bpo-44089.IoANsN.rst
@@ -0,0 +1,2 @@
+Allow subclassing ``csv.Error`` in 3.10 (it was allowed in 3.9 and earlier but
+was disallowed in early versions of 3.10).
diff --git a/Modules/_csv.c b/Modules/_csv.c
index cade1ca9d47..bdb67fdb487 100644
--- a/Modules/_csv.c
+++ b/Modules/_csv.c
@@ -1515,7 +1515,7 @@ static PyType_Slot error_slots[] = {
 
 PyType_Spec error_spec = {
     .name = "_csv.Error",
-    .flags = Py_TPFLAGS_DEFAULT,
+    .flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE,
     .slots = error_slots,
 };