Pass multiple bash arrays to Python using argparse

Question

I have a Python script that I want to run from a bash, and it needs multiple string arrays/lists inputs. This answer by lorenzog in another question explains how to do it with one array, and it works fine. But how can I pass multiple arrays? Here's what I've tried so far:

Bash script:

#!/bin/bash

declare -a first=("one" "two" "three")
declare -a second=("four" "five")
declare -a third=("six")
declare -a fourth=("seven" "eight")

python argsprob.py "${first[@]}" "${second[@]}" "${third[@]}" "${fourth[@]}"

Python script:

#!/usr/bin/env python3

import argparse

parser = argparse.ArgumentParser()
parser.add_argument('first', nargs='+')
parser.add_argument('second', nargs='+')
parser.add_argument('third', nargs='+')
parser.add_argument('fourth', nargs='+')
args = parser.parse_args()

print(args.first)
print(args.second)
print(args.third)
print(args.fourth)

Output

$ bash argsprob.sh
['one', 'two', 'three', 'four', 'five']
['six']
['seven']
['eight']

Desired output

['one','two','three']
['four','five']
['six']
['seven','eight']

As you can probably tell I have no idea what I'm doing. I've tried other ways of using argparse (more arguments, different "nargs", etc) but none of them works. Any help is appreciated!

Look at sys.argv. I think your bash command expands the arrays in to one long list of strings. So argparse has no idea of where your original first ends and second begins. It allocates one string each for the last 3 arguments (because of their '+'), and allocates the rest to the first. — hpaulj
– hpaulj, Commented Mar 14, 2018 at 16:47
Another option is to make the arguments flagged (optionals). Then the flags ('--first', etc) act as delimiters between the arrays. — hpaulj
– hpaulj, Commented Mar 14, 2018 at 16:50
@hpaulj Chaginc nargs to 3,2,1,2 worked, but this makes things harder when I don't know how many elements the lists have. Second method you said worked perfectly! Thank you! If you answer I can mark it as solved — lanadaquenada
– lanadaquenada, Commented Mar 14, 2018 at 16:56

0xc0de · Accepted Answer · 2019-05-08 08:15:30Z

1

With:

import argparse
import sys
print(sys.argv[1:])
parser = argparse.ArgumentParser()
parser.add_argument('--first', nargs='+')
parser.add_argument('--second', nargs='+')
parser.add_argument('--third', nargs='+')
parser.add_argument('--fourth', nargs='+')
args = parser.parse_args()
print(args)

the call:

1948:~/mypy$ python stack49282913.py --first "${first[@]}" --second "${second[@]}" --th "${third[@]}" --fo "${fourth[@]}"

['--first', 'one', 'two', 'three', '--second', 'four', 'five', '--th', 'six', '--fo', 'seven', 'eight']

Namespace(first=['one', 'two', 'three'], fourth=['seven', 'eight'], second=['four', 'five'], third=['six'])

edited May 8, 2019 at 8:15

0xc0de

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answered Mar 16, 2018 at 2:51

hpaulj

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