def check_conflict(opt):
    """
    >>> check_conflict({'app': 'foobar'})
    >>> try:
    ...     check_conflict({'from': 'bbb'})
    ... except:
    ...     pass
    Error: Conflict field found, {from: bbb}
    """
    reserved_words = ['target', 'from', 'checkout', 'file']
    for rw in reserved_words:
        if rw in opt:
            print(f'Error: Conflict field found, {{{rw}: {opt.get(rw)}}}')
            exit(1)
