Extremely bare bones JSONDecodeError snippet renderer

invalid.json

{
    "foo": [
        1,
        2,
        3,
    ]
}

json_trace.py

import json
import sys

with open(sys.argv[1]) as f:
    try:
        doc = json.load(f)
    except json.JSONDecodeError as exc:
        print(f'JSON error: {exc.args[0]}', file=sys.stderr)
        snippet_start   = exc.doc.rfind('\n', 0, exc.pos-exc.colno)
        snippet_end     = exc.doc.find('\n', exc.pos)
        print(exc.doc[snippet_start:snippet_end], file=sys.stderr)
        print((exc.colno-1)*'~' + '^', file=sys.stderr)
        sys.exit(1)

$ python3 json_trace.py invalid.json 
JSON error: Expecting value: line 6 column 5 (char 52)

        3,
    ]
~~~~^