optparse在python中使用的用法消息字符串？

parser.error(...)

parser

OptionParser

from optparse import OptionParser

parser = OptionParser('usage: %prog [options] target source [source ...]')
[...]

(opts, args) = parser.parse_args()

if len(args) < 2:
    parser.error('need a target and at least one source')

Usage: merge-into.py [options] target source [source ...]

merge-into.py: error: need a target and at least one source

parser.format_help()