Python: How to make an option to be required in optparse?

Question

I\'ve read this http://docs.python.org/release/2.6.2/library/optparse.html

But I\'m not so clear how to make an option to be required in optparse?

I\'ve tried to

Answer 1

The current answer with the most votes would not work if, for example, the argument were an integer or float for which zero is a valid input. In these cases it would say that there is an error. An alternative (to add to the several others here) would be to do e.g.

parser = OptionParser(usage='usage: %prog [options] arguments')
parser.add_option('-f', '--file', dest='filename')
(options, args) = parser.parse_args()
if 'filename' not in options.__dict__:
  parser.error('Filename not given')

Answer 2

Since if not x doesn't work for some(negative,zero) parameters,

and to prevent lots of if tests, i preferr something like this:

required="host username password".split()

parser = OptionParser()
parser.add_option("-H", '--host', dest='host')
parser.add_option("-U", '--user', dest='username')
parser.add_option("-P", '--pass', dest='password')
parser.add_option("-s", '--ssl',  dest='ssl',help="optional usage of ssl")

(options, args) = parser.parse_args()

for r in required:
    if options.__dict__[r] is None:
        parser.error("parameter %s required"%r)

Answer 3

There are at least two methods of implementing required options with optparse. As mentioned in the docs page, optparse doesn’t prevent you from implementing required options, but doesn’t give you much help at it either. Find below the examples found in files distributed with the source.

Although please note that optparse module is deprecated since version 2.7 and will not be developed further. You should use argparse module instead.

---

Version 1: Add a method to OptionParser which applications must call after parsing arguments:

import optparse

class OptionParser (optparse.OptionParser):

    def check_required (self, opt):
      option = self.get_option(opt)

      # Assumes the option's 'default' is set to None!
      if getattr(self.values, option.dest) is None:
          self.error("%s option not supplied" % option)


parser = OptionParser()
parser.add_option("-v", action="count", dest="verbose")
parser.add_option("-f", "--file", default=None)
(options, args) = parser.parse_args()

print "verbose:", options.verbose
print "file:", options.file
parser.check_required("-f")

Source: docs/lib/required_1.txt

---

Version 2: Extend Option and add a required attribute; extend OptionParser to ensure that required options are present after parsing:

import optparse

class Option (optparse.Option):
    ATTRS = optparse.Option.ATTRS + ['required']

    def _check_required (self):
        if self.required and not self.takes_value():
            raise OptionError(
                "required flag set for option that doesn't take a value",
                 self)

    # Make sure _check_required() is called from the constructor!
    CHECK_METHODS = optparse.Option.CHECK_METHODS + [_check_required]

    def process (self, opt, value, values, parser):
        optparse.Option.process(self, opt, value, values, parser)
        parser.option_seen[self] = 1


class OptionParser (optparse.OptionParser):

    def _init_parsing_state (self):
        optparse.OptionParser._init_parsing_state(self)
        self.option_seen = {}

    def check_values (self, values, args):
        for option in self.option_list:
            if (isinstance(option, Option) and
                option.required and
                not self.option_seen.has_key(option)):
                self.error("%s not supplied" % option)
        return (values, args)


parser = OptionParser(option_list=[
    Option("-v", action="count", dest="verbose"),
    Option("-f", "--file", required=1)])
(options, args) = parser.parse_args()

print "verbose:", options.verbose
print "file:", options.file

Source: docs/lib/required_2.txt