Displaying better error message than No JSON object could be decoded

Question

Python code to load data from some long complicated JSON file   with open filename   r   as f    data   json loads f read       note  the best code version should be   with open filename   r   as f    data   json load f    but both exhibit similar behavior   For many types of JSON error  missing delimiters  incorrect backslashes in strings  etc   this prints a nice helpful message containing the line and column number where the JSON error was found   However  for other types of JSON error  including the classic  using comma on the last item in a list   but also other things like capitalising true false   Python s output is just   Traceback  most recent call last     File  myfile py   line 8  in myfunction     config   json loads f read      File  c  python27 lib json   init   py   line 326  in loads     return  default decoder decode s    File  c  python27 lib json decoder py   line 360  in decode     obj  end   self raw decode s  idx  w s  0  end      File  c  python27 lib json decoder py   line 378  in raw decode     raise ValueError  No JSON object could be decoded   ValueError  No JSON object could be decoded   For that type of ValueError  how do you get Python to tell you where is the error in the JSON file

User · Answer

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']

User · Answer

Trailing commas is recognized as a non-standard JSON format  which is recognized as the correct format under the RFC 8259 RFC 7159 standard  you can verify it here JSON Formatter Validator   but there will be warnings  However  it is being parsed Sometimes  Trailing commas will be abnormal

User · Answer

The accepted answer is the easiest one to fix the problem  But in case you are not allowed to install the simplejson due to your company policy  I propose below solution to fix the particular issue of  using comma on the last item in a list     Create a child class  JSONLintCheck  to inherite from class  JSONDecoder  and override the init method of the class  JSONDecoder  like below    def   init   self  encoding None  object hook None  parse float None parse int None  parse constant None  strict True object pairs hook None                  super JSONLintCheck self    init   encoding None  object hook None       parse float None parse int None  parse constant None  strict True object pairs hook None          self scan once   make scanner self        make scanner is a new function that used to override the  scan once  method of the above class  And here is code for it        1    usr bin env python   2 from json import JSONDecoder   3 from json import decoder   4 import re   5   6 NUMBER RE   re compile    7     r  -    0  1-9  d       d     eE  -    d        8      re VERBOSE   re MULTILINE   re DOTALL     9  10 def py make scanner context    11     parse object   context parse object  12     parse array   context parse array  13     parse string   context parse string  14     match number   NUMBER RE match  15     encoding   context encoding  16     strict   context strict  17     parse float   context parse float  18     parse int   context parse int  19     parse constant   context parse constant  20     object hook   context object hook  21     object pairs hook   context object pairs hook  22  23     def  scan once string  idx    24         try   25             nextchar   string idx   26         except IndexError   27             raise ValueError decoder errmsg  Could not get the next character  string idx    28              raise StopIteration  29  30         if nextchar          31             return parse string string  idx   1  encoding  strict   32         elif nextchar          33             return parse object  string  idx   1   encoding  strict   34                  scan once  object hook  object pairs hook   35         elif nextchar          36             return parse array  string  idx   1    scan once   37         elif nextchar     n  and string idx idx   4      null    38             return None  idx   4  39         elif nextchar     t  and string idx idx   4      true    40             return True  idx   4  41         elif nextchar     f  and string idx idx   5      false    42             return False  idx   5  43  44         m   match number string  idx   45         if m is not None   46             integer  frac  exp   m groups    47             if frac or exp   48                 res   parse float integer    frac or        exp or       49             else   50                 res   parse int integer   51             return res  m end    52         elif nextchar     N  and string idx idx   3      NaN    53             return parse constant  NaN    idx   3  54         elif nextchar     I  and string idx idx   8      Infinity    55             return parse constant  Infinity    idx   8  56         elif nextchar     -  and string idx idx   9      -Infinity    57             return parse constant  -Infinity    idx   9  58         else   59              raise StopIteration     Here is where needs modification  60             raise ValueError decoder errmsg  Expecting propert name enclosed in double quotes  string idx    61     return  scan once  62  63 make scanner   py make scanner    Better put the  make scanner  function together with the new child class into a same file

User · Answer

I had a similar problem this was my code       json file json dumps pyJson      file   open  list json   w       file write json file         json file   open  list json   r       json decoded   json load json file      print json decoded   the problem was i had forgotten to file close    I did it and fixed the problem

User · Answer

For my particular version of this problem  I went ahead and searched the function declaration of load json file path  within the packaging py file  then smuggled a print line into it   def load json file path       data   open path   r   read       print data     try          return Bunch json loads data       except ValueError  e          raise MalformedJsonFileError   s when reading   s      str e                                                                  path     That way it would print the content of the json file before entering the try-catch  and that way     even with my barely existing Python knowledge     I was able to quickly figure out why my configuration couldn t read the json file   It was because I had set up my text editor to write a UTF-8 BOM     stupid   Just mentioning this because  while maybe not a good answer to the OP s specific problem  this was a rather quick method in determining the source of a very oppressing bug  And I bet that many people will stumble upon this article who are searching a more verbose solution for a MalformedJsonFileError  No JSON object could be decoded when reading      So that might help them

User · Answer

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

User · Answer

Just hit the same issue and in my case the problem was related to BOM  byte order mark  at the beginning of the file    json tool would refuse to process even empty file  just curly braces  until i removed the UTF BOM mark   What I have done is    opened my json file with vim  removed byte order mark  set nobomb  save file   This resolved the problem with json tool  Hope this helps

User · Answer

When your file is created  Instead of creating a file with content is empty  Replace with   json dump     file

User · Answer

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

User · Answer

As to me  my json file is very large  when use common json in python it gets the above error   After install simplejson by sudo pip install simplejson   And then  I solved it   import json import simplejson   def test parse json        f path     home hello  data json      with open f path  as f            j data   json load f         ValueError  No JSON object could be decoded         j data   simplejson load f     right     lst img   j data  images    image       print lst img 0    if   name         main         test parse json

User · Answer

I had a similar problem and it was due to singlequotes  The JSON standard http   json org  talks only about using double quotes so it must be that the python json library supports only double quotes

User · Answer

You could use cjson  that claims to be up to 250 times faster than pure-python implementations  given that you have  some long complicated JSON file  and you will probably need to run it several times  decoders fail and report the first error they encounter only

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

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