from typeguard import typechecked


@typechecked
def replace_str_in_fil(old_fil: str, new_fil: str, tgt: str, repl: str):
    """
    old_fil: old file.
    tgt: str to be replaced.
    repl: replacement.
    new_fil: upd'ed file.

    Replaces tgt in old file.
    Saves upd'ed file.
    """
    # read old file
    with open(old_fil, "r") as f:
        lines = f.read()

    # replace target str
    new_lines = lines.replace(tgt, repl)

    # save upd'ed file
    with open(new_fil, "w") as f:
        f.write(new_lines)