From 55dda07578142b532f74292ef136c4556863ff1a Mon Sep 17 00:00:00 2001
From: Anton Petnitsky <168552591+Mukller@users.noreply.github.com>
Date: Wed, 29 Jul 2026 19:44:00 +0300
Subject: [PATCH 1/3] fix(parser): raise ParserMatchError instead of IndexError
 for malformed fmt (#1191)

DateTimeParser.parse() iterates over fmt_tokens and calls
match.group(token) for each one. When the format string is malformed,
the generated regex may not define a named capture group for every
token. In that case match.group(token) raises IndexError (not KeyError),
which propagates up as an unhandled exception.

Wrap the match.group() block in try/except IndexError and re-raise
as ParserMatchError, consistent with how the no-match case is handled
just above the loop.
---
 arrow/parser.py | 21 +++++++++++++++------
 1 file changed, 15 insertions(+), 6 deletions(-)

diff --git a/arrow/parser.py b/arrow/parser.py
index fc3774b09..d0d7abce2 100644
--- a/arrow/parser.py
+++ b/arrow/parser.py
@@ -422,12 +422,21 @@ def parse(
         parts: _Parts = {}
         for token in fmt_tokens:
             value: Union[Tuple[str, str, str], str]
-            if token == "Do":
-                value = match.group("value")
-            elif token == "W":
-                value = (match.group("year"), match.group("week"), match.group("day"))
-            else:
-                value = match.group(token)
+            try:
+                if token == "Do":
+                    value = match.group("value")
+                elif token == "W":
+                    value = (
+                        match.group("year"),
+                        match.group("week"),
+                        match.group("day"),
+                    )
+                else:
+                    value = match.group(token)
+            except IndexError:
+                raise ParserMatchError(
+                    f"Failed to match {fmt!r} when parsing {datetime_string!r}."
+                )
 
             if value is None:
                 raise ParserMatchError(

From e51c0ddd8cecacad60726fa215625e93f0469f6b Mon Sep 17 00:00:00 2001
From: Anton Petnitsky <168552591+Mukller@users.noreply.github.com>
Date: Wed, 29 Jul 2026 23:06:35 +0300
Subject: [PATCH 2/3] test(parser): add regression for #1191 (IndexError ->
 ParserMatchError for Do token)

On locales whose ordinal_day_re does not expose a named value capture group
(e.g. GermanLocale, which inherits the base r"(\d+)"), match.group("value")
inside the Do-token branch previously propagated as a bare IndexError.
After the fix it becomes ParserMatchError.
---
 tests/test_parser.py | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/tests/test_parser.py b/tests/test_parser.py
index 7038d880f..9a7facf1d 100644
--- a/tests/test_parser.py
+++ b/tests/test_parser.py
@@ -529,6 +529,14 @@ def test_parse_with_leading_and_trailing_whitespace(self):
 
         assert self.parser.parse("      2016      ", "YYYY") == datetime(2016, 1, 1)
 
+    def test_parse_Do_indexerror_becomes_parser_match_error(self):
+        """Regression for #1191: On locales whose ordinal_day_re does not expose
+        a named 'value' capture group (e.g. GermanLocale), match.group('value')
+        previously raised a bare IndexError. It must raise ParserMatchError."""
+        de_parser = DateTimeParser(locale="de")
+        with pytest.raises(ParserMatchError):
+            de_parser.parse("1", "Do")
+
         assert self.parser.parse(
             "      2016-05-16 04:05:06.789120      ", "YYYY-MM-DD hh:mm:ss.S"
         ) == datetime(2016, 5, 16, 4, 5, 6, 789120)

From 5aeb4c61ddc5a5ddb5ef4d301f9b691cd8fd0348 Mon Sep 17 00:00:00 2001
From: Anton Petnitsky <168552591+Mukller@users.noreply.github.com>
Date: Thu, 13 Aug 2026 00:27:40 +0300
Subject: [PATCH 3/3] ci: retrigger CI to clear transient windows/pypy network
 failure