Displaying better error message than "No JSON object could be decoded"

Solution 1:

I've found that the simplejson module gives more descriptive errors in many cases where the built-in json module is vague. For instance, for the case of having a comma after the last item in a list:

json.loads('[1,2,]')
....
ValueError: No JSON object could be decoded

which is not very descriptive. The same operation with simplejson:

simplejson.loads('[1,2,]')
...
simplejson.decoder.JSONDecodeError: Expecting object: line 1 column 5 (char 5)

Much better! Likewise for other common errors like capitalizing True.

Solution 2:

You wont be able to get python to tell you where the JSON is incorrect. You will need to use a linter online somewhere like this

This will show you error in the JSON you are trying to decode.

Solution 3:

You could try the rson library found here: http://code.google.com/p/rson/ . I it also up on PYPI: https://pypi.python.org/pypi/rson/0.9 so you can use easy_install or pip to get it.

for the example given by tom:

>>> rson.loads('[1,2,]')
...
rson.base.tokenizer.RSONDecodeError: Unexpected trailing comma: line 1, column 6, text ']'

RSON is a designed to be a superset of JSON, so it can parse JSON files. It also has an alternate syntax which is much nicer for humans to look at and edit. I use it quite a bit for input files.

As for the capitalizing of boolean values: it appears that rson reads incorrectly capitalized booleans as strings.

>>> rson.loads('[true,False]')
[True, u'False']