gh-151021: Fix mmap empty searches past the end (GH-151023)

esadomer · web-flow · commit f2cab7b0cf01 · 2026-06-07T16:01:24.000+03:00
diff --git a/Lib/test/test_mmap.py b/Lib/test/test_mmap.py
@@ -354,6 +354,8 @@ def test_find_end(self):
         self.assertEqual(m.find(b'one', 1, -1), 8)
         self.assertEqual(m.find(b'one', 1, -2), -1)
         self.assertEqual(m.find(bytearray(b'one')), 0)
+        self.assertEqual(m.find(b'', n + 1), -1)
+        self.assertEqual(m.rfind(b'', n + 1), -1)
 
         for i in range(-n-1, n+1):
             for j in range(-n-1, n+1):
diff --git a/Misc/NEWS.d/next/Library/2026-06-06-15-20-54.gh-issue-151021.J4qk2A.rst b/Misc/NEWS.d/next/Library/2026-06-06-15-20-54.gh-issue-151021.J4qk2A.rst
@@ -0,0 +1,3 @@
+Fix :meth:`mmap.mmap.find` and :meth:`~mmap.mmap.rfind` to return ``-1``
+when searching for an empty subsequence with a start position past the end
+of the mapping.
diff --git a/Modules/mmapmodule.c b/Modules/mmapmodule.c
@@ -620,8 +620,6 @@ mmap_gfind_lock_held(mmap_object *self, Py_buffer *view, PyObject *start_obj,
         start += self->size;
     if (start < 0)
         start = 0;
-    else if (start > self->size)
-        start = self->size;
 
     if (end < 0)
         end += self->size;

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,3 @@`
	`1`	+Fix :meth:`mmap.mmap.find` and :meth:`~mmap.mmap.rfind` to return ``-1``
	`2`	`+when searching for an empty subsequence with a start position past the end`
	`3`	`+of the mapping.`