How do I use the 'json' module to read in one JSON object at a time?

json, python

Solution

Generally speaking, putting more than one JSON object into a file makes that file invalid, broken JSON. That said, you can still parse data in chunks using the `JSONDecoder.raw_decode()` method.

The following will yield complete objects as the parser finds them:

from json import JSONDecoder
from functools import partial


def json_parse(fileobj, decoder=JSONDecoder(), buffersize=2048):
    buffer = ''
    for chunk in iter(partial(fileobj.read, buffersize), ''):
         buffer += chunk
         while buffer:
             try:
                 result, index = decoder.raw_decode(buffer)
                 yield result
                 buffer = buffer[index:].lstrip()
             except ValueError:
                 # Not enough data to decode, read more
                 break

This function will read chunks from the given file object in `buffersize` chunks, and have the `decoder` object parse whole JSON objects from the buffer. Each parsed object is yielded to the caller.

Use it like this:

with open('yourfilename', 'r') as infh:
    for data in json_parse(infh):
        # process object

Use this only if your JSON objects are written to a file back-to-back, with no newlines in between. If you do have newlines, and each JSON object is limited to a single line, you have a JSON Lines document, in which case you can use Loading and parsing a JSON file with multiple JSON objects in Python instead.

Problem

Original source

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• Loading and parsing a JSON file with multiple JSON objects