argparse argument order

Question

I have a little problem.

I use argparse to parse my arguments, and it's working very well.

To have the args, I do :

p_args = parser.parse_args(argv)
args = dict(p_args._get_kwargs())

But the problem with p_args is that I don't know how to get these arguments ordered by their position in the command line, because it's a dict.

So is there any possibility to have the arguments in a tuple/list/ordered dict by their order in the command line?

Answer 1

To keep arguments ordered, I use a custom action like this:

import argparse
class CustomAction(argparse.Action):
    def __call__(self, parser, namespace, values, option_string=None):
        if not 'ordered_args' in namespace:
            setattr(namespace, 'ordered_args', [])
        previous = namespace.ordered_args
        previous.append((self.dest, values))
        setattr(namespace, 'ordered_args', previous)
parser = argparse.ArgumentParser()
parser.add_argument('--test1', action=CustomAction)
parser.add_argument('--test2', action=CustomAction)

To use it, for example:

>>> parser.parse_args(['--test2', '2', '--test1', '1'])
Namespace(ordered_args=[('test2', '2'), ('test1', '1')], test1=None, test2=None)

Answer 2

If you need to know the order in which the arguments appear in your parser, you can set up the parser like this:

import argparse

parser = argparse.ArgumentParser(description = "A cool application.")
parser.add_argument('--optional1')
parser.add_argument('positionals', nargs='+')
parser.add_argument('--optional2')

args = parser.parse_args()
print args.positionals

Here's a quick example of running this code:

$ python s.py --optional1 X --optional2 Y 1 2 3 4 5
['1', '2', '3', '4', '5']

Note that args.positionals is a list with the positional arguments in order. See the argparse documentation for more information.

Answer 3

This is a bit fragile since it relies on understanding the internals of argparse.ArgumentParser, but in lieu of rewriting argparse.ArgumentParser.parse_known_args, here's what I use:

class OrderedNamespace(argparse.Namespace):
    def __init__(self, **kwargs):
        self.__dict__["_arg_order"] = []
        self.__dict__["_arg_order_first_time_through"] = True
        argparse.Namespace.__init__(self, **kwargs)

    def __setattr__(self, name, value):
        #print("Setting %s -> %s" % (name, value))
        self.__dict__[name] = value
        if name in self._arg_order and hasattr(self, "_arg_order_first_time_through"):
            self.__dict__["_arg_order"] = []
            delattr(self, "_arg_order_first_time_through")
        self.__dict__["_arg_order"].append(name)

    def _finalize(self):
        if hasattr(self, "_arg_order_first_time_through"):
            self.__dict__["_arg_order"] = []
            delattr(self, "_arg_order_first_time_through")

    def _latest_of(self, k1, k2):
        try:
            print self._arg_order
            if self._arg_order.index(k1) > self._arg_order.index(k2):
                return k1
        except ValueError:
            if k1 in self._arg_order:
                return k1
        return k2

This works through the knowledge that argparse.ArgumentParser.parse_known_args runs through the entire option list once setting default values for each argument. Meaning that user specified arguments begin the first time __setattr__ hits an argument that it's seen before.

Usage:

options, extra_args = parser.parse_known_args(sys.argv, namespace=OrderedNamespace())

You can check options._arg_order for the order of user specified command line args, or use options._latest_of("arg1", "arg2") to see which of --arg1 or --arg2 was specified later on the command line (which, for my purposes was what I needed: seeing which of two options would be the overriding one).

UPDATE: had to add _finalize method to handle pathological case of sys.argv() not containing any arguments in the list)

Answer 4

There is module especially made to handle this :

https://github.com/claylabs/ordered-keyword-args

without using orderedkwargs module

def multiple_kwarguments(first , **lotsofothers):
    print first

    for i,other in lotsofothers:
         print other
    return True

multiple_kwarguments("first", second="second", third="third" ,fourth="fourth" ,fifth="fifth")

output:

first
second
fifth
fourth
third

On using orderedkwargs module

from orderedkwargs import ordered kwargs  
@orderedkwargs  
def mutliple_kwarguments(first , *lotsofothers):
    print first

    for i, other in lotsofothers:
        print other
    return True


mutliple_kwarguments("first", second="second", third="third" ,fourth="fourth" ,fifth="fifth")

Output:

first
second
third
fourth
fifth

Note: Single asterik is required while using this module with decorator above the function.

Answer 5

I needed this because, for logging purposes, I liked to print the arguments after they were parsed. The problem was that the arguments are not printed in order, which was really annoying.

The custom action class just flat out did not work for me. I had other arguments which used a different action such as 'store_true' and default arguments also don't work since the custom action class is not called if the argument is not given in the command line. What worked for me was creating a wrapper class like this:

import collections

from argparse import ArgumentParser

class SortedArgumentParser():
    def __init__(self, *args, **kwargs):
        self.ap = ArgumentParser(*args, **kwargs)
        self.args_dict = collections.OrderedDict()      

    def add_argument(self, *args, **kwargs):
        self.ap.add_argument(*args, **kwargs)
        # Also store dest kwarg
        self.args_dict[kwargs['dest']] = None

    def parse_args(self):
        # Returns a sorted dictionary
        unsorted_dict = self.ap.parse_args().__dict__
        for unsorted_entry in unsorted_dict:
            self.args_dict[unsorted_entry] = unsorted_dict[unsorted_entry]

        return self.args_dict

The pros are that the add_argument method should have the exact same functionality as the original ArgumentParser. The cons are that if you want other methods you will have to write wrapped for all of them. Luckily for me all I ever used was add_argument and parse_args, so this served my purposes pretty well. You would also need to do more work if you wanted to use parent ArgumentParsers.