Fixes errors in invalid JSON. Running time is (length of input) x (number of errors).

fix_invalid_json.py

#!/usr/bin/env python
import json
import sys


def run(filename):
    with open(filename) as f:
        s = f.read()

    # This code will re-read the file from the beginning after fixing each error, which is slow. A better solution
    # would be to write/extend a JSON parser that can fix errors as it reads the data in a single pass.
    #
    # If the errors occur in predictable locations (e.g. control characters only occur inside strings and can therefore
    # all be escaped), then string substitution and regular expressions can be used.
    #
    # Inspired by https://stackoverflow.com/questions/18514910/how-do-i-automatically-fix-an-invalid-json-string
    while True:
        try:
            result = json.loads(s)
            break
        except Exception as e:
            if e.msg not in (
                # Occurs after an unescaped quote character followed by a non-comma.
                "Expecting ',' delimiter",
                # Occurs after an unescaped quote character followed by a comma.
                "Expecting property name enclosed in double quotes",
                # Occurs for unescaped characters like tab, etc.
                "Invalid control character at",
            ):
                # Print any errors we can't handle, to be added to this code.
                print(repr([str(e), s[s.rindex('"', 0, e.pos - 1):s.index('"', e.pos) + 2]]), file=sys.stderr)
                break

            if e.msg in ("Expecting ',' delimiter", "Expecting property name enclosed in double quotes"):
                # If the quote character is followed by whitespace, the error position will not be immediately after
                # the quote character, so we search backwards for it.
                unescaped = s.rindex('\"', 0, e.pos)
                replacement = r'\"'
            elif e.msg == "Invalid control character at":
                unescaped = e.pos
                replacement = json.dumps(s[e.pos])[1:-1]

            s = s[:unescaped] + replacement + s[unescaped + 1:]
            print('.', end='', file=sys.stderr, flush=True)

    print(result)


if __name__ == '__main__':
    run(sys.argv[1])