Lejlek Lejlek - 4 months ago 39
JSON Question

Retrieving JSON objects from a text file (using Python)

I have thousands of text files containing multiple JSON objects, but unfortunately there is no delimiter between the objects. Objects are stored as dictionaries and some of their fields are themselves objects. Each object might have a variable number of nested objects. Concretely, an object might look like this:

{field1: {}, field2: "some value", field3: {}, ...}


and hundreds of such objects are concatenated without a delimiter in a text file. This means that I can neither use
json.load()
nor
json.loads()
.

Any suggestion on how I can solve this problem. Is there a known parser to do this?

Answer

This decodes your "list" of JSON Objects from a string:

from json import JSONDecoder

def loads_invalid_obj_list(s):
    decoder = JSONDecoder()
    s_len = len(s)

    objs = []
    end = 0
    while end != s_len:
        obj, end = decoder.raw_decode(s, idx=end)
        objs.append(obj)

    return objs

The bonus here is that you play nice with the parser. Hence it keeps telling you exactly where it found an error.

Examples

>>> loads_invalid_obj_list('{}{}')
[{}, {}]

>>> loads_invalid_obj_list('{}{\n}{')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "decode.py", line 9, in loads_invalid_obj_list
    obj, end = decoder.raw_decode(s, idx=end)
  File     "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/json/decoder.py", line 376, in raw_decode
    obj, end = self.scan_once(s, idx)
ValueError: Expecting object: line 2 column 2 (char 5)

Clean Solution (added later)

import json
import re

#shameless copy paste from json/decoder.py
FLAGS = re.VERBOSE | re.MULTILINE | re.DOTALL
WHITESPACE = re.compile(r'[ \t\n\r]*', FLAGS)

class ConcatJSONDecoder(json.JSONDecoder):
    def decode(self, s, _w=WHITESPACE.match):
        s_len = len(s)

        objs = []
        end = 0
        while end != s_len:
            obj, end = self.raw_decode(s, idx=_w(s, end).end())
            end = _w(s, end).end()
            objs.append(obj)
        return objs

Examples

>>> print json.loads('{}', cls=ConcatJSONDecoder)
[{}]

>>> print json.load(open('file'), cls=ConcatJSONDecoder)
[{}]

>>> print json.loads('{}{} {', cls=ConcatJSONDecoder)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/json/__init__.py", line 339, in loads
    return cls(encoding=encoding, **kw).decode(s)
  File "decode.py", line 15, in decode
    obj, end = self.raw_decode(s, idx=_w(s, end).end())
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/json/decoder.py", line 376, in raw_decode
    obj, end = self.scan_once(s, idx)
ValueError: Expecting object: line 1 column 5 (char 5)
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