append into json

[scidam]

This is minimal example.

In [1]: import json

In [2]: ds = """
   ...: {"tag": [1, 2, 3]}
   ...: """

In [3]: js = json.loads(ds)

In [4]: js['tag'].append(4)

In [5]: json.dumps(js)
Out[5]: '{"tag": [1, 2, 3, 4]}'

Could you show, what did you try so far?