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Metavar: It provides a different name for optional argument in help messages.
Optparse module makes easy to write command-line tools. It allows argument parsing in the python program. optparse make it easy to handle the command-line argument. It comes default with python. It allows dynamic data input to change the output.
optparse is a more convenient, flexible, and powerful library for parsing command-line options than the old getopt module. optparse uses a more declarative style of command-line parsing: you create an instance of OptionParser , populate it with options, and parse the command line.
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.
metavar seems to be used for generating help : http://www.python.org/doc/2.5.2/lib/optparse-generating-help.html
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