[3.14] gh-142787: Handle empty sqlite3 blob slices (GH-142824) (#145297)

(cherry picked from commit 06b0920)

Co-authored-by: A.Ibrahim <abdulrasheedibrahim47@gmail.com>

Author: miss-islington

Lib/test/test_sqlite3/test_dbapi.py

@@ -1387,6 +1387,11 @@ def test_blob_get_slice(self):
     def test_blob_get_empty_slice(self):
         self.assertEqual(self.blob[5:5], b"")
 
+    def test_blob_get_empty_slice_oob_indices(self):
+        self.cx.execute("insert into test(b) values (?)", (b"abc",))
+        with self.cx.blobopen("test", "b", 2) as blob:
+            self.assertEqual(blob[5:-5], b"")
+
     def test_blob_get_slice_negative_index(self):
         self.assertEqual(self.blob[5:-5], self.data[5:-5])
 

Misc/NEWS.d/next/Library/2025-12-16-13-34-48.gh-issue-142787.wNitJX.rst

@@ -0,0 +1,2 @@
+Fix assertion failure in :mod:`sqlite3` blob subscript when slicing with
+indices that result in an empty slice.

Modules/_sqlite/blob.c

@@ -434,6 +434,10 @@ subscript_slice(pysqlite_Blob *self, PyObject *item)
         return NULL;
     }
 
+    if (len == 0) {
+        return PyBytes_FromStringAndSize(NULL, 0);
+    }
+
     if (step == 1) {
         return read_multiple(self, len, start);
     }