def decompose_code(code):
    """Decompose a MARC "code" into tag, ind1, ind2, subcode."""
    code = '%-6s' % code
    ind1 = code[3:4]
    if ind1 == ' ':
        ind1 = '_'
    ind2 = code[4:5]
    if ind2 == ' ':
        ind2 = '_'
    subcode = code[5:6]
    if subcode == ' ':
        subcode = None
    return code[0:3], ind1, ind2, subcode
