keep proto when it is an output in graph (#177)

* keep proto when it is an output in graph

* remove redundant list

Author: fumihwh

onnx_tf/frontend.py

@@ -309,11 +309,14 @@ def tensorflow_graph_to_onnx_graph(cls,
           make_tensor_value_info(output_name, output_onnx_type,
                                  output.attr["_output_shapes"][i]))
 
-    inputs = list(chain.from_iterable(map(lambda p: list(p.input), ops_proto)))
-
-    # Remove proto in inputs_proto and consts_proto if proto is not used as input in ONNX
-    inputs_proto = list(filter(lambda x: x.name in inputs, inputs_proto))
-    consts_proto = list(filter(lambda x: x.name in inputs, consts_proto))
+    inputs = list(chain.from_iterable(map(lambda p: p.input, ops_proto)))
+    outputs = list(map(lambda p: p.name, output_proto))
+    in_out = inputs + outputs
+
+    # Remove proto in inputs_proto and consts_proto
+    # if proto is not used as input or an output in ONNX
+    inputs_proto = list(filter(lambda x: x.name in in_out, inputs_proto))
+    consts_proto = list(filter(lambda x: x.name in in_out, consts_proto))
 
     inputs_proto = cls._data_type_caster(inputs_proto, data_type_cast_map)
     consts_proto = cls._data_type_caster(consts_proto, data_type_cast_map)