Question

I am not sure what optparse‘s metavar parameter is used for. I see it is used all around, but I can’t see its use.

Can someone make it clear to me? Thanks.

Answer 1

As @Guillaume says, it’s used for generating help. If you want to have an option that takes an argument, such as a filename, you can add the metavar parameter to the add_option call so your preferred argument name/descriptor is output in the help message. From the current module documentation:

usage = 'usage: %prog [options] arg1 arg2' parser = OptionParser(usage=usage) parser.add_option('-f', '--filename',                   metavar='FILE', help='write output to FILE'), 

would produce help like this:

usage: <yourscript> [options] arg1 arg2  options:   -f FILE, --filename=FILE 

The ‘FILE’ after the ‘-f’ and the ‘–filename’ comes from the metavar.