ValueError: substring not found

[DeaD_EyE]

Regex could be a solution:

import re


def on_off_finder(in_string):
    values = ("off", "on")
    # index   [ 0 ]  [ 1]
    # bool(0) -> False
    # bool(1) -> True
    if match := re.search(r"ch=(on|off)", in_string.lower()):
        # it does only match, if ch=on or ch=off was
        # in_string.lower()
        # then getting the group1, which is in parentheses
        # then searching the index for off/on
        # converting the index (0 or 1) into bool
        # return this value
        return bool(values.index(match.group(1)))
    else:
        # ch=on or ch=off was not in_string.lower()
        return False

To check the regex, visit: https://regex101.com/
Don't forget to select on the left side Python

Joke: If you have a problem and want to solve it with regex, then you have two problems.