CODEWITHSUNDEEP
python
Ian Sudbery
Ian Sudbery

Reputation: 1738

Listing choices in optparse help output

When you generate help for an option with Python's optparse module, you can use the %defualt placeholder to insert the default value for the option into the help. It there anyway of doing the same thing for the valid choices when the type is choice?

E.g something like:

import optparse
parser=optparse.OptionParser()
parser.add_option("-m","--method",
                  type = "choice", choices = ("method1","method2","method3"),
                  help = "Method to use. Valid choices are %choices. Default: %default")

Upvotes: 4

Views: 3096

Answers (3)

msvalkon
msvalkon

Reputation: 12077

argparse prints the choices by default, as you can see in the demo below. One way to print the defaults automatically is to use the ArgumentsDefaultHelpFormatter.

import argparse

parser = argparse.ArgumentParser(formatter_class=argparse.ArgumentDefaultsHelpFormatter)
parser.add_argument("-m","--method", type=str, choices=("method1","method2","method3"),
              default="method1", help = "Method to use.")

parser.parse_args()

DEMO: 

msvalkon@Lunkwill:/tmp$ python test.py -h
usage: test.py [-h] [-m {method1,method2,method3}]

optional arguments:
  -h, --help            show this help message and exit
  -m {method1,method2,method3}, --method {method1,method2,method3}
                        Method to use. (default: method1)

Upvotes: 1

alecxe
alecxe

Reputation: 474191

As @msvalkon commented, optparse is deprecated - use argparse instead.

You can specify %(choices)s placeholder in the help argument:

import argparse


parser = argparse.ArgumentParser()
parser.add_argument("-m",
                    "--method",
                    type=str,
                    choices=("method1", "method2", "method3"),
                    help = "Method to use. Valid choices are %(choices)s. Default: %(default)s",
                    default="method1")

parser.parse_args()

Here's what on the console:

$ python test.py --help
usage: test.py [-h] [-m {method1,method2,method3}]

optional arguments:
  -h, --help            show this help message and exit
  -m {method1,method2,method3}, --method {method1,method2,method3}
                        Method to use. Valid choices are method1, method2,
                        method3. Default: method1

Upvotes: 2

Adrian Ratnapala
Adrian Ratnapala

Reputation: 5733

I assume your problem is that you don't want to repeat the list of choices. Fortunately variables are universal if sometimes ugly solution to this kind of problem. So the ugly-but-pragmatic answer is:

import optparse

choices_m = ("method1","method2","method3")
default_m = "method_1"

parser=optparse.OptionParser()
parser.add_option("-m","--method",
                  type = "choice", choices = choices_m, 
                  default = defult_m,
                  help = "Method to use. Valid choices are %s. Default: %s"\
                         % (choices_m, default_m)

And of course this kind of thing can be done using argparse too.

Upvotes: 3

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