def split_arg(s, sep, default=''):
    """
    split str s in two at first sep, returning empty string as second result if no sep
    """
    r = s.split(sep, 2)
    r = list(map(str.strip, r))
    arg = r[0]
    if len(r) == 1:
        val = default
    else:
        val = r[1]
        val = {'true': True, 'false': False}.get(val.lower(), val)
    return arg, val
