Convert bool values to string in json.dumps()

If it were me, I'd convert the Python data structure to the required format and then call json.dumps():

import json
import sys

def convert(obj):
    if isinstance(obj, bool):
        return str(obj).lower()
    if isinstance(obj, (list, tuple)):
        return [convert(item) for item in obj]
    if isinstance(obj, dict):
        return {convert(key):convert(value) for key, value in obj.items()}
    return obj

dct = {
  "is_open": True
}
print (json.dumps(dct))
print (json.dumps(convert(dct)))

Output:

{"is_open": true}
{"is_open": "true"}