Using parser_args values to feed a for loop (Python 3.6)

Question

I am trying to create a script that takes multiple command line arguments of the same type, and then feeds them into a for loop for processing, the below is what I have in my code:

import argparse

parser = argparse.ArgumentParser(description='XYZ')
parser.add_argument('[values]', nargs='+', help='A list of values')

u = parser.parse_args(['3crlV5QaiuUjRz5kWze', 'F9Xw0rggHZ_PLs62q'])

for values in u:
    ... # do a bunch of stuff for each "value"

I understand that the values stored in parse_args are a NAMESPACE, hence the error below when I run my code:

TypeError: 'Namespace' object is not iterable

Is there any way to turn them into a list object? so that I can pass them to my for loop, or is there any other approach I should be using? Just getting started with python, so apologies in advance if this is a noob question

What type of values do you want to iterate?

willeM_ Van Onsem
– willeM_ Van Onsem

2017-01-23 03:57:05 +00:00
Commented Jan 23, 2017 at 3:57 — willeM_ Van Onsem
– willeM_ Van Onsem, Commented Jan 23, 2017 at 3:57

falsetru · Accepted Answer · 2017-01-23 03:57:31Z

2

You need to iterate u.values (the argument name you specified in add_argument call) not u itself; To do that you need to rename [values] to values:

import argparse

parser = argparse.ArgumentParser(description='XYZ')
parser.add_argument('values', nargs='+', help='A list of values')
#                   ^^^^^^^^

u = parser.parse_args(['3crlV5QaiuUjRz5kWze', 'F9Xw0rggHZ_PLs62q'])

for value in u.values:
    #        ^^^^^^^^
    # do a bunch of stuff for each "value"

answered Jan 23, 2017 at 3:57

falsetru

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1 Comment

anthony sottile Over a year ago

A note in case anybody else comes along this question, though the question is tagged python3.x (and mentions python3.6) this solution works in python2.7+

hpaulj · Accepted Answer · 2017-01-23 04:56:56Z

The values from parsing are in a simple of object of class argparse.namespace (which can be customized - see the docs).

Usually you access those values by attribute name, e.g. args.foo. For unusual names you many have to use getattr(args, '[values]').

In the simple case argument values are a single string or number. With nargs like '*' or '+', the values will be in a list. With append action type you may even get lists within lists.

I encourage users to print the args namespace.

In [2]: parser = argparse.ArgumentParser(description='XYZ')
   ...: parser.add_argument('[values]', nargs='+', help='A list of values')....
In [3]: args =parser.parse_args(['3crlV5QaiuUjRz5kWze', 'F9Xw0rggHZ_PLs62q'])

In [4]: print(args)
Namespace([values]=['3crlV5QaiuUjRz5kWze', 'F9Xw0rggHZ_PLs62q'])

With your 'dest' I have to use the getattr to fetch the list of strings from args.

In [5]: getattr(args,'[values]')
Out[5]: ['3crlV5QaiuUjRz5kWze', 'F9Xw0rggHZ_PLs62q']

args is a simple object, so you can add attributes or modify existing ones. e.g.

In [6]: args.values = ['3crlV5QaiuUjRz5kWze', 'F9Xw0rggHZ_PLs62q']
In [7]: print(args)
Namespace([values]=['3crlV5QaiuUjRz5kWze', 'F9Xw0rggHZ_PLs62q'], 
    values=['3crlV5QaiuUjRz5kWze', 'F9Xw0rggHZ_PLs62q'])

If you are more familiar with dictionaries, you can use vars():

In [9]: vars(args)['values']
Out[9]: ['3crlV5QaiuUjRz5kWze', 'F9Xw0rggHZ_PLs62q']

Play around with this sort of thing an interactive Python session.

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