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optparse: simulating ‘–help’

Summary

Getting optparse to show a summary of script options under program control.

What do you use optparse for ?

optparse is a Python standard library for parsing command-line options.

optparse provides a relatively simple way of

* defining a set of command line arguments which the user may enter
* parsing the command line entered and storing the results of the parse

I need help !

By default optparse will respond to a either of :

<yourscript> -h

or

<yourscript> --help

by printing a summary of your scripts options.

What I learned today

In the script I was working on today I wanted to respond to the user not entering any argument at all by printing a summary of all options available (in other words as if they user had entered ‘–help’ or ‘-h’ as an argument).

There is a way you can do this but for some reason it’s not in the list of OptionParser methods shown in the documentation.

print_help()

If you call the method ‘print_help’ as shown in the code below optparse will respond by by printing the same text that would be shown if the user were to enter an argument of ‘–help’.

parser = OptionParser(description=desc, usage=usage)
parser.add_option(  "-i", "--inbox", action="store",  dest="inbox",
metavar="INBOX", help="Location of INBOX")
parser.add_option(  "-o", "--outpath", action="store", dest="outpath",
metavar="PATH", help="PATH to output csv file")
parser.add_option(  "-v", "--verbose", action="store_true",
dest="verbose", help="Show each file processed")

(options, args) = parser.parse_args()

if (options.inbox is None) and (options.outpath is None):
  parser.print_help()
  exit(-1)
elif not os.path.exists(options.inbox):
  parser.error('inbox location does not exist')
elif not os.path.exists(os.path.dirname(options.outpath)):
  parser.error('path to ouput location does not exist')

return options