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Click here to download version 0.2 of jsaone.

Click here for the (64 bit) Debian/Ubuntu package (Python 2).

Click here for the (64 bit) Debian/Ubuntu package (Python 3).

What is jsaone?

This is a tiny wrapper around the json module in the Python standard library, allowing to read a json file incrementally.

This can be useful for

  • parsing json streams without waiting for the end of the transmission,
  • parsing very big json objects without wasting RAM for the json representation itself.

It is an alternative to ijson (written when I did not know ijson existed, but in the end more efficient).


No extensive tests were made (if you make them, let me know), but here are the results (in seconds) obtained in opening a local file with 384650 objects, totalling 174 MB:

Parser Iteration 1 Iteration 2
standard (non-incremental) json 9.511 9.273
cythonized jsaone 19.055 18.956
ijson (with yajl2 backend) 62.250 64.538
pure python jsaone 421.641 421.821

Those results were obtained with the script “tests/”.

Clearly those numbers are affected by the speed of the CPU and of the medium/stream. In particular, since the test was made on a file from a local hard disk, the bottleneck was clearly the CPU, and hence it is disadvantageous for incremental parsers (including jsaone). If the bottleneck is given by the medium/stream, jsaone should even outperform the standard json, which will start processing only after the entire stream is received.

Why "jsaone"

Because it sounds similar to “json”… but the Saône is a (large) stream.



  1. If you use Debian or a derivative (such as Ubuntu or Mint), you can simply use the packages provided above.
  2. jsaone is on pypi, so you can install it with pip install jsaone
  3. you can extract/clone the git repo, then move in the “jsaone” folder and give the command
python3 build_ext --inplace

(replace “python3” with “python” if you are using Python 2).


import jsaone
with open('/path/to/my/file.json') as f:
    gen = jsaone.load(f)
    for key, val in gen:


You can browse the git repo here or clone with

git clone

For bugs and enhancements, just write me - - ideally pointing to a git branch solving the issue/providing an enhancement.

Jsaone should be able to parse any compliant json string… so if you find one on which it fails, please let me know!


Released under the GPL 3. Feel free to contact me if this is a problem for you (and GPL 2 is not).

jsaone.txt · Ultima modifica: 2019/02/05 19:16 da pietro