python · serhiy-storchaka · Jun 4, 2026 · Jun 4, 2026
@@ -1431,6 +1431,18 @@ def test_blob_set_empty_slice(self):
        self.blob[0:0] = b""
        self.assertEqual(self.blob[:], self.data)

+    def test_blob_set_empty_slice_wrong_type(self):
+        with self.assertRaises(TypeError):
+            self.blob[5:5] = None
+
+    def test_blob_set_empty_slice_wrong_size(self):
+        with self.assertRaisesRegex(IndexError, "wrong size"):
+            self.blob[5:5] = b"123"
+
+    def test_blob_set_empty_slice_correct(self):
+        self.blob[5:5] = b""
+        self.assertEqual(self.blob[:], self.data)
+
    def test_blob_set_slice_with_skip(self):
        self.blob[0:10:2] = b"12345"
        actual = self.cx.execute("select b from test").fetchone()[0]

diff --git a/Misc/NEWS.d/next/Library/2026-06-04-21-49-18.gh-issue-150913.EmptyBl.rst b/Misc/NEWS.d/next/Library/2026-06-04-21-49-18.gh-issue-150913.EmptyBl.rst
@@ -0,0 +1,3 @@
+Fix :class:`sqlite3.Blob` slice assignment to raise
+:exc:`TypeError` and :exc:`IndexError` for type and size mismatches
+respectively, even when the target slice is empty.
@@ -517,21 +517,25 @@ ass_subscript_slice(pysqlite_Blob *self, PyObject *item, PyObject *value)
        return -1;
    }

-    if (len == 0) {
-        return 0;
-    }
-
    Py_buffer vbuf;
    if (PyObject_GetBuffer(value, &vbuf, PyBUF_SIMPLE) < 0) {
        return -1;
    }

-    int rc = -1;
    if (vbuf.len != len) {
        PyErr_SetString(PyExc_IndexError,
                        "Blob slice assignment is wrong size");
+        PyBuffer_Release(&vbuf);
+        return -1;
    }
-    else if (step == 1) {
+
+    if (len == 0) {
+        PyBuffer_Release(&vbuf);
+        return 0;
+    }
+
+    int rc = -1;
+    if (step == 1) {
        rc = inner_write(self, vbuf.buf, len, start);
    }
    else {