Object of type 'RepeatedCompositeContainer' is not JSON serializable

Question

Using Google Client Library interacting with the vision library.

I have a function to detect labels from an image.

GoogleVision.py

import os

from google.cloud import vision
from google.cloud.vision import types
from google.protobuf.json_format import MessageToJson


class GoogleVision():

    def detectLabels(self, uri):

        client = vision.ImageAnnotatorClient()
        image = types.Image()
        image.source.image_uri = uri

        response = client.label_detection(image=image)
        labels = response.label_annotations

        return labels

I have an api to call this function.

from flask_restful import Resource
from flask import request
from flask import json
from util.GoogleVision import GoogleVision

import os


class Vision(Resource):

    def get(self):

        return {"message": "API Working"}

    def post(self):

        googleVision = GoogleVision()

        req = request.get_json()

        url = req['url']

        result = googleVision.detectLabels(url)

        return result

However, it does not return the result and errors with the following

TypeError: Object of type 'RepeatedCompositeContainer' is not JSON serializable

"RepeatedCompositeContainer" comes from "protobuf" and as far as I can see, you are not using `MessageToJson`. Here you can see a [question](https://github.com/GoogleCloudPlatform/google-cloud-python/issues/3485#issuecomment-307797562) where it was recommended to use it or use dictionaries. Also, I saw this [SO question](https://stackoverflow.com/questions/20001229/how-to-get-posted-json-in-flask) to get json from Flask. — Iñigo, Jul 16 '18 at 11:30
MessageToJson did not work either, there are questions about this that already exist. — Kay, Jul 16 '18 at 12:44
@AkashJobanputra i ended up doing a for loop over the result and creating my own object — Kay, Jul 24 '18 at 11:46
Would be nice if @Iñigo if you could provide a working solution. — Kay, Jul 24 '18 at 11:47
@Kay I found the solution here, https://github.com/GoogleCloudPlatform/google-cloud-python/issues/3485#issuecomment-406194079 — Akash Jobanputra, Jul 24 '18 at 11:47

Vishal K · Answer 1 · 2021-08-05T14:06:16.860

This question was answered in this GitHub link, which might help to resolve your issue.

The error you encountered is

TypeError: Object of type 'RepeatedCompositeContainer' is not JSON serializable

Below is the solution provided in the GitHub thread

The Vision library returns plain protobuf objects, which can be serialized to JSON using:

from google.protobuf.json_format import MessageToJson
serialized = MessageToJson(original)

You can also go to dictionaries using something like protobuf3-to-dict.

Object of type 'RepeatedCompositeContainer' is not JSON serializable

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