diff --git a/mace/python/tools/mace_engine_factory_codegen.py b/mace/python/tools/mace_engine_factory_codegen.py
index ce91006506cecc14d2838a880f5c5398e8676886..5518deb34afb1a5201fe037220535b7b0577b6cb 100644
--- a/mace/python/tools/mace_engine_factory_codegen.py
+++ b/mace/python/tools/mace_engine_factory_codegen.py
@@ -27,9 +27,10 @@ def gen_mace_engine_factory(model_tags, template_dir,
         loader=FileSystemLoader(template_dir), trim_blocks=True)
     # generate mace_run BUILD file
     template_name = 'mace_engine_factory.h.jinja2'
+    model_tags = list(model_tags)
     source = j2_env.get_template(template_name).render(
         model_tags=model_tags,
         embed_model_data=embed_model_data,
     )
-    with open(output_dir + '/mace_engine_factory.h', "wb") as f:
+    with open(output_dir + '/mace_engine_factory.h', "w") as f:
         f.write(source)
diff --git a/mace/python/tools/model_saver.py b/mace/python/tools/model_saver.py
index 56709ef69c4b65b7c45f93fa4587472fad245115..117bb8ef60a1481ae55613e90146fa57faced977 100644
--- a/mace/python/tools/model_saver.py
+++ b/mace/python/tools/model_saver.py
@@ -216,7 +216,7 @@ def save_model_to_code(net_def, model_tag, runtime,
             tensor=tensor,
             tag=model_tag,
         )
-        with open(output_dir + 'tensor' + str(counter) + '.cc', "wb") as f:
+        with open(output_dir + 'tensor' + str(counter) + '.cc', "w") as f:
             f.write(source)
         counter += 1
 
@@ -228,7 +228,7 @@ def save_model_to_code(net_def, model_tag, runtime,
             tag=model_tag,
             model_data_size=len(model_data),
             model_data=model_data)
-        with open(output_dir + 'tensor_data' + '.cc', "wb") as f:
+        with open(output_dir + 'tensor_data' + '.cc', "w") as f:
             f.write(source)
 
     # generate op source files
@@ -243,7 +243,7 @@ def save_model_to_code(net_def, model_tag, runtime,
             tag=model_tag,
             runtime=runtime,
         )
-        with open(output_dir + 'op' + str(counter) + '.cc', "wb") as f:
+        with open(output_dir + 'op' + str(counter) + '.cc', "w") as f:
             f.write(source)
         counter += 1
 
@@ -262,13 +262,13 @@ def save_model_to_code(net_def, model_tag, runtime,
         winograd_conv=winograd_conv,
         checksum=checksum,
         build_time=build_time)
-    with open(output_dir + 'model.cc', "wb") as f:
+    with open(output_dir + 'model.cc', "w") as f:
         f.write(source)
 
     # generate model header file
     template_name = 'model_header.jinja2'
     source = j2_env.get_template(template_name).render(tag=model_tag, )
-    with open(output_dir + model_tag + '.h', "wb") as f:
+    with open(output_dir + model_tag + '.h', "w") as f:
         f.write(source)
 
 
diff --git a/mace/python/tools/operator.jinja2 b/mace/python/tools/operator.jinja2
index fc77b1e67aedbd34513442870b910c9332c8786d..e3492ddf7f112fef067c1b51ef7ba83b3065711d 100644
--- a/mace/python/tools/operator.jinja2
+++ b/mace/python/tools/operator.jinja2
@@ -80,7 +80,7 @@ void CreateOperator{{i}}(mace::OperatorDef *op) {
   arg->set_i({{ arg.i }});
   {%- endif %}
   {%- if arg.HasField('s') %}
-  arg->set_s({{ arg.s|tojson }});
+  arg->set_s({{ arg.s.decode('utf-8')|tojson }});
   {%- endif %}
 
   arg->mutable_floats()->Reserve({{ arg.floats|length }});
@@ -161,4 +161,3 @@ void CreateOperator{{i}}(mace::OperatorDef *op) {
 
 }  // namespace {{tag}}
 }  // namespace mace
-