Case insensitive argparse choices

Question

Is it possible to check argparse choices in case-insensitive manner?

import argparse
choices = [\"win64\", \"win32\"]
parser = argparse.ArgumentParser()
pars         


        

Answer 1

Keeping the case information would also be possible with a one liner:

type = lambda arg: {x.lower(): x for x in choices}[arg.lower()],

Where choices would be the same list as passed to the choices parameter.

Answer 2

Using lower in the type is nice way of doing this, if you don't mind loosing the case information.

If you want to retain the case, you could define a custom choices class. The choices needs two methods, __contains__ (for testing in), and iteration (to list the choices).

class mylist(list):
    # list subclass that uses lower() when testing for 'in'
    def __contains__(self, other):
        return super(mylist,self).__contains__(other.lower())
choices=mylist(['win64','win32'])
parser = argparse.ArgumentParser()
parser.add_argument("-p", choices=choices)
print(parser.parse_args(["-p", "Win32"]))
# Namespace(p='Win32')

The help is:

usage: ipython [-h] [-p {win64,win32}]

optional arguments:
  -h, --help        show this help message and exit
  -p {win64,win32}

Answer 3

Transform the argument into lowercase by using

type = str.lower

for the -p switch.

This solution was pointed out by chepner in a comment. The solution I proposed earlier was

type = lambda s : s.lower()

which is also valid, but it's simpler to just use str.lower.