Usage message string that optparse makes in python?

I use optparse module to parse the options that I ma开发者_如何学运维ke, and it automatically generates usage message to print with -h option.

How can I get the usage message as a string in a python script? I'd like to print out it when something's wrong with parsing.

If you use parser.error(...) (where parser is your OptionParser object) you'll get your usage message.

For example:

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')

produces:

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

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

How about parser.format_help()?