Read JSON formatted string in Python

Question

I have a simple Websockets server in python, it receives messages from Android app clients, I tried to make the message payload from the client in JSON but I felt. It is only working when it is in String. One solution I found is to keep the message string but with JSON format:

try {
    json.put("name", "Jack");
    json.put("age", "24");
    message = json.toString(2);
} catch (JSONException e) {
    e.printStackTrace();
}

webSocket.send(message);

Inspired by the Javascript JSON.stringify(message)

I printed the message on the server and it seems to be formatted

My question is how can I reverse back it into JSON on the server when it received?

I tried this way in Python:

def on_message(self,message):
    data = json.loads(message)
    self.write_message(data['name'])

but I got this error:

ERROR:tornado.application:Uncaught exception in /
Traceback (most recent call last):
  File "/usr/local/lib/python3.4/dist-packages/tornado/websocket.py", line 494, in _run_callback
    result = callback(*args, **kwargs)
  File "index.py", line 24, in on_message
    data = json.loads(message)
  File "/usr/lib/python3.4/json/__init__.py", line 318, in loads
    return _default_decoder.decode(s)
  File "/usr/lib/python3.4/json/decoder.py", line 343, in decode
    obj, end = self.raw_decode(s, idx=_w(s, 0).end())
  File "/usr/lib/python3.4/json/decoder.py", line 361, in raw_decode
    raise ValueError(errmsg("Expecting value", s, err.value)) from None
ValueError: Expecting value: line 1 column 1 (char 0)

The json documentation shows examples to encode and decode json, i.e. going from json to string and vice versa — Francesco Montesano
– Francesco Montesano, Commented Sep 19, 2017 at 13:20
Printing the value of message given to json.loads() will be very helpful. — norok2
– norok2, Commented Sep 19, 2017 at 13:37
You should really try to print it from within the function. It seems you are calling it with an empty string value for message. For example, json.loads('') gives a very similar error in my installation. — norok2
– norok2, Commented Sep 19, 2017 at 14:07

GLR · Accepted Answer · 2017-09-19 13:20:31Z

1

You should use the json Python package. To have a JSON, you could simply do import json and json.dumps(message).

answered Sep 19, 2017 at 13:20

GLR

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1 Comment

Hussein Over a year ago

I tried, but it did not work, I updated the question with the error.

NIKHIL RANE · Accepted Answer · 2017-09-19 13:23:24Z

1

Use a Json package in python

import json
data = json.loads(your_var)

In data variable you get a json format data

hope this will help you

answered Sep 19, 2017 at 13:23

NIKHIL RANE

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1 Comment

Hussein Over a year ago

I tried, but it did not work, I updated the question with the error.

norok2 · Accepted Answer · 2017-09-19 14:16:04Z

1

Will something like this work for you?

import json

# assume this is the JSON you receive
text = json.dumps(dict(name='Jack', age='24'))

# show the text to be converted
print(text)
# outputs: {"name": "Jack", "age": "24"}

# load a string and convert to Python object
# see `json` module more for details
obj = json.loads(text)

edited Sep 19, 2017 at 14:16

answered Sep 19, 2017 at 13:22

norok2

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4 Comments

Hussein Over a year ago

I tried, but it did not work, I updated the question with the error.

norok2 Over a year ago

can you print the value of message?

Hussein Over a year ago

I could, and It gives me the message formatted as I send it. But I don't know how to re-parse it again into JSON

norok2 Over a year ago

if you could show, it may be easier to spot the issue. Maybe it is some custom formatting or whitespace or something silly like that.

Hussein · Accepted Answer · 2017-09-19 14:13:32Z

0

I tried this way and it worked for me, I converted the message into a dictionary using ast and then used the new message as I wanted:

    formattedMessage = ast.literal_eval(format(message))
    self.write_message(formattedMessage["name"])

answered Sep 19, 2017 at 14:13

Hussein

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1 Comment

norok2 Over a year ago

If the source is a json text, this is going to produce very fragile code. I would rather make sure that a proper JSON parser works. simplejson is known to produce more informative error messages, if that helps you.

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