86

I want to pass a list of names into my program written in Python from console. For instance, I would like to use a way similar to this (I know it shouldn't work because of bash):

$ python myprog.py -n name1 name2

So, I tried this code:

# myprog.py

from argparse import ArgumentParser

parser = ArgumentParser()
parser.add_argument('-n', '--names-list', default=[])
args = parser.parse_args()

print(args.names_list) # I need ['name1', 'name2'] here

That led to the error:

usage: myprog.py [-h] [-n NAMES_LIST]
myprog.py: error: unrecognized arguments: name2

I know I could pass the names with quotes "name1 name2" and split it in my code args.names_list.split(). But I'm curious, is there a better way to pass the list of strings via argparse module.

Any ideas would be appreciated.

Thanks!

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4 Answers 4

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111

You need to define --names-list to take an arbitrary number of arguments.

parser.add_argument('-n', '--names-list', nargs='+', default=[])

Note that options with arbitrary number of arguments don't typically play well with positional arguments, though:

# Is this 4 arguments to -n, or
# 3 arguments and a single positional argument, or ...
myprog.py -n a b c d
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3 Comments

not possible with the --arg=value syntax? like --arg="one, two, three" or similar without splitting?
The OP already acknowledged that the string could be split after parse_args is called.
This answer misses how the parsed arguments are queried in python code.
17

You need to use nargs:

parser.add_argument('-n', '--names-list', nargs="*")

https://docs.python.org/3/library/argparse.html#nargs

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1 Comment

This answer misses how the argument is called on terminal and how the parsed arguments are queried in python code.
7

Another option is to repeat the argument on the command line.

To do this, change the action to append.

parser.add_argument('-n', '--names-list', action="append")

From the terminal you can call:

python myprog.py -n name1 -n name2 -n name3

And the result will be:

Namespace(n=['name1', 'name2', 'name3'])
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1 Comment

This is an elegant solution!
3 
parser.add_argument('-n', '--names-list', default=[], nargs='+')
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1 Comment

Please add some more information. How does the call on command line looks like? How to query the parsed arguments?

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