JSONDecodeError in `onnxmltools.utils.save_text` function

Hi! I am wondering about onnxmltools.utils.save_text function. The example on title page says:

# Save as text
onnxmltools.utils.save_text(onnx_model, 'example.json')

So I expected the output file to be a valid JSON but it is not. Here is the example code copied from the title page; MWE:

import onnxmltools
from keras.layers import Input, Dense, Add
from keras.models import Model

# N: batch size, C: sub-model input dimension, D: final model's input dimension
N, C, D = 2, 3, 3

# Define a sub-model, it will become a part of our final model
sub_input1 = Input(shape=(C,))
sub_mapped1 = Dense(D)(sub_input1)
sub_model1 = Model(inputs=sub_input1, outputs=sub_mapped1)

# Define another sub-model, it will become a part of our final model
sub_input2 = Input(shape=(C,))
sub_mapped2 = Dense(D)(sub_input2)
sub_model2 = Model(inputs=sub_input2, outputs=sub_mapped2)

# Define a model built upon the previous two sub-models
input1 = Input(shape=(D,))
input2 = Input(shape=(D,))
mapped1_2 = sub_model1(input1)
mapped2_2 = sub_model2(input2)
sub_sum = Add()([mapped1_2, mapped2_2])
keras_model = Model(inputs=[input1, input2], output=sub_sum)

# Convert it! The target_opset parameter is optional.
onnx_model = onnxmltools.convert_keras(keras_model, target_opset=7) 

onnxmltools.utils.save_text(onnx_model, 'example.json')

import json
with open('example.json') as f:
    json.load(f)

yields error: JSONDecodeError: Expecting value: line 1 column 1 (char 0)

So… can I somehow obtain a valid JSON out of converted ONNX model?

[jiafatom]

@Eugene-1984 onnx_model is a protobuf object not a json, so json.load should not work. The function save_text is a legacy code, we need deprecate it, just use save_model to save it into binary file. This library does not support the conversion to json.

[vinitra-zz]

@Eugene-1984 The following script should help you get started! Remember to pip install protobuf and pip install onnx in your environment.

from google.protobuf.json_format import MessageToJson
import onnx
import json

model = onnx.load('model.onnx')
jsonObj = MessageToJson(model)

with open('model.json', 'w') as outfile:
    json.dump(jsonObj, outfile)

with open('model.json') as infile:
    j_model = json.load(infile)

j_model is now a json string with the contents of model.json. If you would prefer the output as a dictionary, please include the following line: dict_model = json.loads(j_model)

See the top voted answer here: https://stackoverflow.com/questions/19734617/protobuf-to-json-in-python