From 1ae18f5963365525cf1506bb4efb616ccff19869 Mon Sep 17 00:00:00 2001
From: Sergey B Kirpichev <skirpichev@gmail.com>
Date: Sun, 6 Apr 2025 14:34:46 +0300
Subject: [PATCH 1/2] gh-130664: support '_' (just as ',') in Decimal's
 formatting

```pycon
>>> from _decimal import Decimal as D
>>> format(D(1234567), '_')
'1_234_567'
>>> format(D(1234567), '020_')
'0_000_000_001_234_567'
>>> format(D('1234.56'), '07_')
'1_234.56'
>>> format(D('1.23456789'), '_')
'1.23456789'
>>> format(D('123.456789'), '_%')
'12_345.6789%'
>>> from _pydecimal import Decimal as D
>>> format(D(1234567), '_')
'1_234_567'
>>> format(D(1234567), '020_')
'0_000_000_001_234_567'
>>> format(D('1234.56'), '07_')
'1_234.56'
>>> format(D('1.23456789'), '_')
'1.23456789'
>>> format(D('123.456789'), '_%')
'12_345.6789%'
```
---
 Lib/_pydecimal.py                                            | 2 +-
 Lib/test/test_decimal.py                                     | 5 +++++
 .../Library/2025-04-06-14-34-29.gh-issue-130664.JF2r-U.rst   | 2 ++
 3 files changed, 8 insertions(+), 1 deletion(-)
 create mode 100644 Misc/NEWS.d/next/Library/2025-04-06-14-34-29.gh-issue-130664.JF2r-U.rst

diff --git a/Lib/_pydecimal.py b/Lib/_pydecimal.py
index ec036199331396..38dc7b70e0f6f0 100644
--- a/Lib/_pydecimal.py
+++ b/Lib/_pydecimal.py
@@ -6098,7 +6098,7 @@ def _convert_for_comparison(self, other, equality_op=False):
 (?P<alt>\#)?
 (?P<zeropad>0)?
 (?P<minimumwidth>(?!0)\d+)?
-(?P<thousands_sep>,)?
+(?P<thousands_sep>[,_])?
 (?:\.(?P<precision>0|(?!0)\d+))?
 (?P<type>[eEfFgGn%])?
 \Z
diff --git a/Lib/test/test_decimal.py b/Lib/test/test_decimal.py
index d2327d247fa498..b97f3ddd4d0ce9 100644
--- a/Lib/test/test_decimal.py
+++ b/Lib/test/test_decimal.py
@@ -1082,6 +1082,11 @@ def test_formatting(self):
             (',%', '123.456789', '12,345.6789%'),
             (',e', '123456', '1.23456e+5'),
             (',E', '123456', '1.23456E+5'),
+            # ... with '_' instead
+            ('_', '1234567', '1_234_567'),
+            ('07_', '1234.56', '1_234.56'),
+            ('_', '1.23456789', '1.23456789'),
+            ('_%', '123.456789', '12_345.6789%'),
 
             # negative zero: default behavior
             ('.1f', '-0', '-0.0'),
diff --git a/Misc/NEWS.d/next/Library/2025-04-06-14-34-29.gh-issue-130664.JF2r-U.rst b/Misc/NEWS.d/next/Library/2025-04-06-14-34-29.gh-issue-130664.JF2r-U.rst
new file mode 100644
index 00000000000000..de199f0f529d78
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2025-04-06-14-34-29.gh-issue-130664.JF2r-U.rst
@@ -0,0 +1,2 @@
+Support ``'_'`` digit separator in formatting of the integral part of
+:class:`~decimal.Decimal`'s.  Patch by Sergey B Kirpichev.

From e0dbe8900303566edb6d177e875049044e1a5a15 Mon Sep 17 00:00:00 2001
From: Sergey B Kirpichev <skirpichev@gmail.com>
Date: Mon, 7 Apr 2025 04:57:21 +0300
Subject: [PATCH 2/2] Update
 Misc/NEWS.d/next/Library/2025-04-06-14-34-29.gh-issue-130664.JF2r-U.rst

Co-authored-by: Stan Ulbrych <89152624+StanFromIreland@users.noreply.github.com>
---
 .../next/Library/2025-04-06-14-34-29.gh-issue-130664.JF2r-U.rst | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Misc/NEWS.d/next/Library/2025-04-06-14-34-29.gh-issue-130664.JF2r-U.rst b/Misc/NEWS.d/next/Library/2025-04-06-14-34-29.gh-issue-130664.JF2r-U.rst
index de199f0f529d78..294a7e031b2806 100644
--- a/Misc/NEWS.d/next/Library/2025-04-06-14-34-29.gh-issue-130664.JF2r-U.rst
+++ b/Misc/NEWS.d/next/Library/2025-04-06-14-34-29.gh-issue-130664.JF2r-U.rst
@@ -1,2 +1,2 @@
-Support ``'_'`` digit separator in formatting of the integral part of
+Support the ``'_'`` digit separator in formatting of the integral part of
 :class:`~decimal.Decimal`'s.  Patch by Sergey B Kirpichev.