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

enter image description here

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)

• Francesco Montesano: The json documentation shows examples to encode and decode json, i.e. going from json to string and vice versa
• norok2: Printing the value of message given to json.loads() will be very helpful.
• norok2: 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.

Answer 1

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

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

Answer 2

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

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

Answer 3

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) 

• Hussein: I tried, but it did not work, I updated the question with the error.
• norok2: can you print the value of message?
• Hussein: 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: 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.

Answer 4

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"])

• norok2: 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.