Python json.loads doesn't work

Question

I've been trying to figure out how to load JSON objects in Python.

   def do_POST(self):
    length = int(self.headers['Content-Length'])
    decData = str(self.rfile.read(length))
    print decData, type(decData)
    "{'name' : 'journal2'}" <type 'str'>
    postData = json.loads(decData)
    print postData, type(postData)
    #{'name' : 'journal2'} <type 'unicode'>
    postData = json.loads(postData)
    print postData, type(postData)
    # Error: Expecting property name enclosed in double quotes

Where am I going wrong?

Error Code (JScript):

var data = "{'name':'journal2'}";
var http_request = new XMLHttpRequest();
http_request.open( "post", url, true );
http_request.setRequestHeader('Content-Type', 'application/json');
http_request.send(data);

True Code (JScript):

var data = '{"name":"journal2"}';
var http_request = new XMLHttpRequest();
http_request.open( "post", url, true );
http_request.setRequestHeader('Content-Type', 'application/json');
http_request.send(JSON.stringify(data));

True Code (Python):

   def do_POST(self):
    length = int(self.headers['Content-Length'])
    decData = self.rfile.read(length)
    postData = json.loads(decData)
    postData = json.loads(postData)

Martijn Pieters · Accepted Answer · 2013-02-08 11:37:50Z

Your JSON data is enclosed in extra quotes making it a JSON string, and the data contained within that string is not JSON.

Print repr(decData) instead, you'll get:

'"{\'name\' : \'journal2\'}"'

and the JSON library is correctly interpreting that as one string with the literal contents {'name' : 'journal2'}. If you stripped the outer quotes, the contained characters are not valid JSON, because JSON strings must always be enclosed in double quotes.

For all the json module is concerned, decData could just as well have contained "This is not JSON" and postData would have been set to u'This is not JSON'.

>>> import json
>>> decData = '''"{'name' : 'journal2'}"'''
>>> json.loads(decData)
u"{'name' : 'journal2'}"
>>> json.loads(json.loads(decData))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/json/__init__.py", line 326, in loads
    return _default_decoder.decode(s)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/json/decoder.py", line 366, in decode
    obj, end = self.raw_decode(s, idx=_w(s, 0).end())
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/json/decoder.py", line 382, in raw_decode
    obj, end = self.scan_once(s, idx)
ValueError: Expecting property name: line 1 column 1 (char 1)

Fix whatever is producing this string, your view is fine, it's the input that is broken.

Sasha Zezulinsky · Accepted Answer · 2015-08-17 10:06:48Z

6

To workaround the error 'Expecting property name enclosed in double quotes' you can do:

import json
data = "{'name' : 'journal2'}"
json.loads(json.dumps(data))

answered Aug 17, 2015 at 10:06

Sasha Zezulinsky

1,8261 gold badge20 silver badges18 bronze badges

2 Comments

WeizhongTu Over a year ago

this is not right, eval(data) may get the right result

J.Serra Over a year ago

That's true but you shouldn't use eval() I think that is the idea of using json module. Use eval is considered a bad practice, I this is an interesting answer about it stackoverflow.com/a/1832957/2289246

Jonathan Leffler · Accepted Answer · 2017-02-20 07:43:17Z

-3

You can also go with eval:

data = "{'name' : 'test'}"
eval(data)

It works and returns you a dict.

edited Feb 20, 2017 at 7:43

Jonathan Leffler

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answered Feb 20, 2017 at 7:36

Manoj Jadhav

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1 Comment

Jonathan Leffler Over a year ago

Judging from the accepted answer, you are starting at the wrong point (you'd need data = '''"{'name' : 'journal2'}"''' to accurately represent what the OP is given), which probably means the eval is less helpful.

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