I am done

rl/Lib/site-packages/onnx/reference/ops/op_flatten.py

@@ -0,0 +1,16 @@
+# Copyright (c) ONNX Project Contributors
+
+# SPDX-License-Identifier: Apache-2.0
+from __future__ import annotations
+
+import numpy as np
+
+from onnx.reference.ops._op import OpRunUnary
+
+
+class Flatten(OpRunUnary):
+    def _run(self, x, axis=None):  # type: ignore
+        i = axis or self.axis  # type: ignore
+        shape = x.shape
+        new_shape = (1, -1) if i == 0 else (np.prod(shape[:i]).astype(int), -1)
+        return (x.reshape(new_shape),)  # type: ignore