Reading named command arguments

Question

Can I use argparse to read named command line arguments that do not need to be in a specific order? I browsed through the documentation but most of it focused on displaying content based on the arguments provided (such as --h).

Right now, my script reads ordered, unnamed arguments:

myscript.py foo-val bar-val

using sys.argv:

foo = sys.argv[1]
bar = sys.argv[2]

But I would like to change the input so that it is order agnostic by naming arguments:

myscript.py --bar=bar-val --foo=foo-val

Solution 1

You can use the Optional Arguments like so:

import argparse, sys

parser=argparse.ArgumentParser()

parser.add_argument('--bar', help='Do the bar option')
parser.add_argument('--foo', help='Foo the program')

args=parser.parse_args()

print args
print sys

Then if you call it with ./prog --bar=bar-val --foo foo-val it prints:

Namespace(bar='bar-val', foo='foo-val')
['Untitled 14.py', '--bar=bar-val', '--foo', 'foo-val']

Or, if the user wants help argparse builds that too:

 $ ./prog -h
usage: Untitled 14.py [-h] [--bar BAR] [--foo FOO]

optional arguments:
  -h, --help  show this help message and exit
  --bar BAR   Do the bar option
  --foo FOO   Foo the program

Solution 2

The answer is yes. A quick look at the argparse documentation would have answered as well.

Here is a very simple example, argparse is able to handle far more specific needs.

import argparse

parser = argparse.ArgumentParser()
parser.add_argument('--foo', '-f', help="a random options", type= str)
parser.add_argument('--bar', '-b', help="a more random option", type= int, default= 0)

print(parser.format_help())
# usage: test_args_4.py [-h] [--foo FOO] [--bar BAR]
# 
# optional arguments:
#   -h, --help         show this help message and exit
#   --foo FOO, -f FOO  a random options
#   --bar BAR, -b BAR  a more random option

args = parser.parse_args("--foo pouet".split())
print(args)  # Namespace(bar=0, foo='pouet')
print(args.foo) # pouet
print(args.bar) # 0

Off course, in a real script, you won't hard-code the command-line options and will call parser.parse_args() (without argument) instead. It will make argparse take the sys.args list as command-line arguments.

You will be able to call this script this way:

test_args_4.py -h  # prints the help message
test_args_4.py -f pouet  # foo="pouet", bar=0 (default value)
test_args_4.py -b 42  # foo=None, bar=42
test_args_4.py -b 77 -f knock  # foo="knock", bar=77

You will discover a lot of other features by reading the doc ;)

Solution 3

I think it might help you with a simple one

#! /usr/bin/python3                                                                                                                    
import sys                                                                                                                             
                                                                                                                                   
keys = ["--paramkey=","-p="]                                                                                                           
for i in range(1,len(sys.argv)):                                                                                                       
    for key in keys:                                                                                                                   
        if sys.argv[i].find(key) == 0:                                                                                                 
            print(f"The Given value is: {sys.argv[i][len(key):]}")                                                                     
            break   

Run:

$ ./example.py --paramkey=paramvalue -p=pvalue

Output:

The Given value is: paramvalue
The Given value is: pvalue 

Comments

[amphibient]

but in your script, you don't know that 'pouet' is passed as the arg value

[amphibient]

how do I read the value of foo after the args have been loaded ?

[amphibient]

is there like args.get('foo') ?

[amphibient]

in line args = parser.parse_args("--foo pouet".split()), why do you hard code what argument value the script should read rather than reading whatever was supplied by the command ?

[dawg]

Use args.bar to read --bar It will return None if not included in the command. You can also use a default instead.

[Tryph]

@amphibient This is an example to show you how to access the arguments values then. in a real script, you will just call parser.parse_args() with no argument and it will take the sys.args list

[DZack]

Using python 3.5.1, and when not included it doesn't return None; it gives an error. So as an alternative, d = vars(args) gives a dictionary (maps named arguments to values)

[dawg]

@MikhailV: Just to show what was on the command line prior to processing with the print sys at the end.

[Mikhail V]

@dawg ah,ok. In python 3 it does not work. It works with print (sys.argv).