Using python ijson to read a large json file with multiple json objects

Question

I\'m trying to parse a large (~100MB) json file using ijson package which allows me to interact with the file in an efficient way. However, after writing some code like this,

Answer 1

Unfortunately the ijson library (v2.3 as of March 2018) does not handle parsing multiple JSON objects. It can only handle 1 overall object, and if you attempt to parse a second object, you will get an error: "ijson.common.JSONError: Additional data". See bug reports here:

• https://github.com/isagalaev/ijson/issues/40
• https://github.com/isagalaev/ijson/issues/42
• https://github.com/isagalaev/ijson/issues/67
• python: how do I parse a stream of json arrays with ijson library

It's a big limitation. However, as long as you have line breaks (new line character) after each JSON object, you can parse each one line-by-line independently, like this:

import io
import ijson

with open(filename, encoding="UTF-8") as json_file:
    cursor = 0
    for line_number, line in enumerate(json_file):
        print ("Processing line", line_number + 1,"at cursor index:", cursor)
        line_as_file = io.StringIO(line)
        # Use a new parser for each line
        json_parser = ijson.parse(line_as_file)
        for prefix, type, value in json_parser:
            print ("prefix=",prefix, "type=",type, "value=",value)
        cursor += len(line)

You are still streaming the file, and not loading it entirely in memory, so it can work on large JSON files. It also uses the line streaming technique from: How to jump to a particular line in a huge text file? and uses enumerate() from: Accessing the index in 'for' loops?

Answer 2

Since the provided chunk looks more like a set of lines each composing an independent JSON, it should be parsed accordingly:

# each JSON is small, there's no need in iterative processing
import json 
with open(filename, 'r') as f:
    for line in f:
        data = json.loads(line)
        # data[u'name'], data[u'engine_speed'], data[u'timestamp'] now
        # contain correspoding values