Passing arguments to a python program from the command line, anything better than sys.argv?

Question

I have a python script that I'd like to run from the terminal, and it takes about 10 numerical arguments. So far the only way i can think of passing the arguments to the program is as follows:

python myscript.py 10,20,30,,40

And then using sys.argv to pick apart the arguments, process them and use them. The thing is, sometimes some of the arguments in the middle need to be blank so that the program uses its "default values" . This means at the moment I need to use commas in the argument to specify a value is blank, which is annoying as its against the standard I've seen for other programs.

Is there a better way of going about this?

Cheers,

Nathan

OS: Ubuntu

python version: 2.7

Maybe store your arguments in a file and then read it from your program is a solution. — zhangyangyu, Apr 06 '13 at 10:47

score 3 · Answer 1 · answered Apr 06 '13 at 12:37

First of all, if you have some arguments that can be omitted, those arguments ought to be options and not real arguments.

Python provides more than one way to parse arguments. The best choice is argparse, which has tons of features and its the module where the development is continuing. If you have to support "old" versions of python then you might be interested in optparse, even though it's been deprecated in python3.2. There exist also a getopt module which mimics C's getopt(do not use this! It's there more for historical reasons and to help people used with these old style of parsing)

A simple example using argparse might be:

import argparse

parser = argparse.ArgumentParser()
parser.add_argument('--option-name', action='store', dest='option_name_var')
parser.add_argument('numbers', type=int, nargs='*')

parsed = parser.parse_args()   #parses sys.argv by default
print(parsed.numbers)
print(parsed.option_name_var)

Which can be used as:

$python example.py 1 2 3
[1, 2, 3]
None
$python example.py 1 2 3  --option-name "value"
[1, 2, 3]
value
$python example.py 1 2 3  --option-name 
usage: example.py [-h] [--option-name OPTION_NAME_VAR] [numbers [numbers ...]]
example.py: error: argument --option-name: expected one argument
$python example.py --option-name 
usage: example.py [-h] [--option-name OPTION_NAME_VAR] [numbers [numbers ...]]
example.py: error: argument --option-name: expected one argument
$python example.py --option-name 5
[]
5
$python example.py 1 2 "string"
usage: example.py [-h] [--option-name OPTION_NAME_VAR] [numbers [numbers ...]]
example.py: error: argument numbers: invalid int value: 'string'

Note how the numbers are automatically converted to a list of integers, and an error is issued if the value is not an integer or there are missing arguments etc.

You also have a default help text:

$python example.py -h
usage: example.py [-h] [--option-name OPTION_NAME_VAR] [numbers [numbers ...]]

positional arguments:
  numbers

optional arguments:
  -h, --help            show this help message and exit
  --option-name OPTION_NAME_VAR

score 0 · Answer 2 · answered Apr 06 '13 at 10:53

0

http://docs.python.org/2/library/argparse.html argparse will be a good choice for you.

answered Apr 06 '13 at 10:53

Yarkee

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Passing arguments to a python program from the command line, anything better than sys.argv?

2 Answers2