Case insensitive argparse choices

Question

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

import argparse choices = ["win64", "win32"] parser = argparse.ArgumentParser() parser.add_argument("-p", choices=choices) print(parser.parse_args(["-p", "Win32"])) 

results in:

usage: choices.py [-h] [-p {win64,win32}] choices.py: error: argument -p: invalid choice: 'Win32' (choose from 'win64','win32') 

Answer 1

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.

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}