save api (pytorch#7097)

Summary:

Tired of writing out this python boilerplate

Reviewed By: tarun292, lucylq

Differential Revision: D66523473

Author: JacobSzwejbka

exir/program/_program.py

@@ -1519,3 +1519,17 @@ def write_to_file(self, open_file: io.BufferedIOBase) -> None:
         reducing the peak memory usage.
         """
         self._pte_data.write_to_file(open_file)
+
+    def save(self, path: str) -> None:
+        """
+        Saves the serialized ExecuTorch binary to the file at `path`.
+        """
+        if path[-4:] != ".pte":
+            logging.error(f"Path {path} does not end with .pte")
+            raise ValueError(f"Path {path} does not end with .pte")
+        try:
+            with open(path, "wb") as file:
+                self.write_to_file(file)
+                logging.info(f"Saved exported program to {path}")
+        except Exception as e:
+            logging.error(f"Error while saving to {path}: {e}")

exir/program/test/test_program.py

@@ -803,3 +803,11 @@ def test_to_edge_with_preserved_ops_not_in_model(self):
         self._test_to_edge_with_preserved_ops(
             program, ops_not_to_decompose, expected_non_decomposed_edge_ops
         )
+
+    def test_save_fails(self):
+        model = TestLinear()
+        program = torch.export.export(model, model._get_random_inputs())
+        edge = to_edge(program)
+        et = edge.to_executorch()
+        with self.assertRaises(ValueError):
+            _ = et.save("/tmp/test_save.pt") # not .pte so should die