From dcbc45f1c952b675395d1a436dcbadee3c48c1db Mon Sep 17 00:00:00 2001
From: gaoflow <148639492+gaoflow@users.noreply.github.com>
Date: Sun, 28 Jun 2026 13:27:54 +0200
Subject: [PATCH] Fix parameterize regex collapsing consecutive multi-character
 separators

When parameterize is called with a multi-character separator (e.g. '__'),
the pattern r'%s{2,}' % re.escape(separator) incorrectly applies the
{2,} quantifier only to the last character of the separator, causing
non-separator characters to be consumed during the collapse step.

For example, with separator '__', the string '___' (one separator plus
one literal underscore) was incorrectly collapsed to '__'.

Fix by wrapping the separator in a (?:...) non-capturing group so the
quantifier applies to the full separator string.
---
 inflection/__init__.py | 2 +-
 test_inflection.py     | 7 +++++++
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/inflection/__init__.py b/inflection/__init__.py
index ffac5ce..a5337c0 100644
--- a/inflection/__init__.py
+++ b/inflection/__init__.py
@@ -277,7 +277,7 @@ def parameterize(string: str, separator: str = '-') -> str:
     if separator:
         re_sep = re.escape(separator)
         # No more than one of the separator in a row.
-        string = re.sub(r'%s{2,}' % re_sep, separator, string)
+        string = re.sub(r'(?:%s){2,}' % re_sep, separator, string)
         # Remove leading/trailing separator.
         string = re.sub(r"(?i)^{sep}|{sep}$".format(sep=re_sep), '', string)
 
diff --git a/test_inflection.py b/test_inflection.py
index f1e64a3..53c04d8 100644
--- a/test_inflection.py
+++ b/test_inflection.py
@@ -402,6 +402,13 @@ def test_parameterize_with_multi_character_separator(
     )
 
 
+def test_parameterize_with_multi_character_separator_partial_collapse() -> None:
+    # Regression test: multi-character separator should not consume
+    # non-separator characters that happen to overlap with separator chars.
+    # '__' is a 2-char separator, so '___' = one separator + one literal '_'.
+    assert 'test___case' == inflection.parameterize('test___case', '__')
+
+
 @pytest.mark.parametrize(
     ("some_string", "parameterized_string"),
     STRING_TO_PARAMETERIZE_WITH_NO_SEPARATOR