Reference : JSON files

Correcting a hand-crafted JSON file to be machine-readable

distpy uses configuration files to make it highly adaptable across hardware and highly flexible in terms of signal processing flows. The JSON format is human-readable text, but we would usually expect the JSON configurations to be constructed by UI rather than by hand.

Due to various "hidden" character types and different character sets, it can sometimes be the case that the JSON configuration files look correct when inspected in an editor but are nevertheless unreadable for python.

If you have this situation during testing, the following code snippet is useful for debugging your configuration files.

import json

filename = "myfileIamTesting.json"

def test(filename):
    with open(filename) as f:
        data = json.load(f)
        print(data)
test()

The results of test() should be a printout of your JSON.

For example, the strainrate2thumbnail.json file should give:

{'document': 0, 'name': 'Standard seismic band thumbnails', 'description': 'Creates pictures of band-limited (5-200 Hz) strain-rate data.', 'command_list': [{'name': 'butter', 'uid': 1, 'in_uid': 0, 'type': 'lowpass', 'freq': 200}, {'name': 'butter', 'uid': 2, 'in_uid': 1, 'type': 'highpass', 'freq': 5}, {'name': 'thumbnail', 'uid': 3, 'in_uid': 2, 'directory_out': 'png'}]}

If the spaces in this file are replaced by tabs, however, you will get something like this:

Traceback (most recent call last):
  File "<pyshell#48>", line 1, in <module>
    test(filename)
  File "<pyshell#47>", line 3, in test
    data = json.load(f)
  File "C:\Python37\lib\json\__init__.py", line 296, in load
    parse_constant=parse_constant, object_pairs_hook=object_pairs_hook, **kw)
  File "C:\Python37\lib\json\__init__.py", line 348, in loads
    return _default_decoder.decode(s)
  File "C:\Python37\lib\json\decoder.py", line 337, in decode
    obj, end = self.raw_decode(s, idx=_w(s, 0).end())
  File "C:\Python37\lib\json\decoder.py", line 353, in raw_decode
    obj, end = self.scan_once(s, idx)
json.decoder.JSONDecodeError: Invalid control character at: line 3 column 20 (char 38)

That final line tells us to look at line 3 column 20 (char 38) in the file. When we examine it and see that it is a tab, we can group replace all occurrences with a space.

In this way that code snippet can help you correct any issues with making a hand-crafted JSON machine-readable.