Python argparse regex expression

Question

Is it possible to use a regex expression for parsing an argument? For example, I want to accept an argument if only it is a 32 length hex (i.e. matches /[a-f0-9A-F]{32}/)

I tried

p.add_argument('hex', type=str, nargs="[a-f0-9A-F]{32}")

without success

Answer 1

This is what the type kwarg is used for: it can take any callable that takes a single string argument and returns the converted value.

import argparse
import re 
from uuid import uuid4

def my_regex_type(arg_value, pat=re.compile(r"^[a-f0-9A-F]{32}$")):
    if not pat.match(arg_value):
        raise argparse.ArgumentTypeError
    return arg_value

parser = argparse.ArgumentParser()
parser.add_argument('hex', type=my_regex_type)

args = parser.parse_args([uuid4().hex])