Python，如何从另一个对象构建一个新的 Json 对象

Question

I've got a Json object with around 10 elements in it. I just need 4 of the 10 elements and would like to place the 4 elements in a new Json object. I tried different ways, but only get errors. My last code:

import json
from pprint import pprint
import time
import datetime

def update_handler(client, update, users, chats):
    #print(update)
    message = str(update)
    data = json.loads(message)
    if data["_"] == "types.UpdateNewMessage":
        from_id = data["message"]["from_id"]
        if from_id == 390189088:
            #output message to screen
            print ("message id: ", data["message"]["id"])
            print ("date/time: ", data["message"]["date"])
            print ("from: ", data["message"]["from_id"])
            print ("message: ", data["message"]["message"])
            print ("**************")
            #output partial message to file
            json_data = {["message"]["id"],["message"]["date"],["message"]["from_id"],["message"]["message"]}
            with open('chartguysalerts.txt', 'a') as outfile:
                json.dump(json_data, outfile)

The last line of that function gives me error: TypeError: list indices must be integers or slices, not str

I can refer to each element separately so they are valid, the output to screen works fine for example. But i don't know how to put them together in a new shorter Json to output to a file.

Answer 1

The easiest way would be to create a list of keys you are interested in and then use a dictionary comprehension:

keys = ['id', 'date', 'from_id', 'message']

new_dict = {key: orig_json_dict['message'][key] for key in keys}