feat(stdlib/sqlite): Implement slice assignment for Blob

ever0de · ever0de · commit 5bdf19c8bb4b · 2025-07-26T23:04:11.000+09:00
diff --git a/Lib/test/test_sqlite3/test_dbapi.py b/Lib/test/test_sqlite3/test_dbapi.py
@@ -1322,8 +1322,6 @@ def test_blob_set_item_with_offset(self):
         expected = b"This blob data string is exactly fifty bytes long."
         self.assertEqual(self.blob.read(), expected)
 
-    # TODO: RUSTPYTHON
-    @unittest.expectedFailure
     def test_blob_set_slice_buffer_object(self):
         from array import array
         self.blob[0:5] = memoryview(b"12345")
@@ -1351,22 +1349,16 @@ def test_blob_get_slice_negative_index(self):
     def test_blob_get_slice_with_skip(self):
         self.assertEqual(self.blob[0:10:2], b"ti lb")
 
-    # TODO: RUSTPYTHON
-    @unittest.expectedFailure
     def test_blob_set_slice(self):
         self.blob[0:5] = b"12345"
         expected = b"12345" + self.data[5:]
         actual = self.cx.execute("select b from test").fetchone()[0]
         self.assertEqual(actual, expected)
 
-    # TODO: RUSTPYTHON
-    @unittest.expectedFailure
     def test_blob_set_empty_slice(self):
         self.blob[0:0] = b""
         self.assertEqual(self.blob[:], self.data)
 
-    # TODO: RUSTPYTHON
-    @unittest.expectedFailure
     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]
@@ -1419,8 +1411,6 @@ def test_blob_set_item_error(self):
         with self.assertRaisesRegex(ValueError, "must be in range"):
             self.blob[0] = 2**65
 
-    # TODO: RUSTPYTHON
-    @unittest.expectedFailure
     def test_blob_set_slice_error(self):
         with self.assertRaisesRegex(IndexError, "wrong size"):
             self.blob[5:10] = b"a"
diff --git a/stdlib/src/sqlite.rs b/stdlib/src/sqlite.rs
@@ -2243,6 +2243,7 @@ mod _sqlite {
             let inner = self.inner(vm)?;
 
             if let Some(index) = needle.try_index_opt(vm) {
+                // Handle single item assignment: blob[i] = b
                 let Some(value) = value.downcast_ref::<PyInt>() else {
                     return Err(vm.new_type_error(format!(
                         "'{}' object cannot be interpreted as an integer",
@@ -2255,11 +2256,63 @@ mod _sqlite {
                 Self::expect_write(blob_len, 1, index, vm)?;
                 let ret = inner.blob.write_single(value, index);
                 self.check(ret, vm)
-            } else if let Some(_slice) = needle.downcast_ref::<PySlice>() {
-                Err(vm.new_not_implemented_error("Blob slice assignment is not implemented"))
-                // let blob_len = inner.blob.bytes();
-                // let slice = slice.to_saturated(vm)?;
-                // let (range, step, length) = slice.adjust_indices(blob_len as usize);
+            } else if let Some(slice) = needle.downcast_ref::<PySlice>() {
+                // Handle slice assignment: blob[a:b:c] = b"..."
+                let value_buf = PyBuffer::try_from_borrowed_object(vm, &value)?;
+
+                let buf = value_buf.as_contiguous().ok_or_else(|| {
+                    vm.new_buffer_error("a contiguous buffer object is required".to_owned())
+                })?;
+
+                let blob_len = inner.blob.bytes();
+                let slice = slice.to_saturated(vm)?;
+                let (range, step, slice_len) = slice.adjust_indices(blob_len as usize);
+
+                if step == 0 {
+                    return Err(vm.new_value_error("step cannot be zero".to_owned()));
+                }
+
+                if buf.len() != slice_len {
+                    return Err(vm.new_index_error("wrong size".to_owned()));
+                }
+
+                if slice_len == 0 {
+                    return Ok(());
+                }
+
+                if step == 1 {
+                    // Fast path for simple slices (step=1).
+                    let ret = inner.blob.write(
+                        buf.as_ptr().cast(),
+                        buf.len() as c_int,
+                        range.start as c_int,
+                    );
+                    self.check(ret, vm)
+                } else {
+                    // "Read-modify-write" strategy for extended slices (step != 1).
+                    let span_len = (range.end - range.start) as usize;
+                    let mut temp_buf = vec![0u8; span_len];
+
+                    let ret = inner.blob.read(
+                        temp_buf.as_mut_ptr().cast(),
+                        span_len as c_int,
+                        range.start as c_int,
+                    );
+                    self.check(ret, vm)?;
+
+                    let mut i_in_temp: usize = 0;
+                    for i_in_src in 0..slice_len {
+                        temp_buf[i_in_temp] = buf[i_in_src];
+                        i_in_temp += step as usize;
+                    }
+
+                    let ret = inner.blob.write(
+                        temp_buf.as_ptr().cast(),
+                        span_len as c_int,
+                        range.start as c_int,
+                    );
+                    self.check(ret, vm)
+                }
             } else {
                 Err(vm.new_type_error("Blob indices must be integers"))
             }
