ConfigParser Issue Reading Leading Tabs vs Spaces

Question

I'm having an issue where I have a config file (which can be edited by non-programmers ... and hence they don't understand the consequences of using a tab vs spaces). The issue is that sometimes they may enter a tab and the configparser seems to mess up when reading the config file. I need to make the script work well with both tabs and leading spaces. Below are a test script, config, and the output.

Python Script (launch with "python3 script_file.py config.cfg"):

import os
import argparse
import configparser

def init():
    ############### READ INPUT ARGS ##################
    parser = argparse.ArgumentParser(description="Test", usage="Parmeters(name)")
    parser.add_argument('configfile', default=None, type=str, help="config file name")
    args = parser.parse_args()

    config_file = os.path.expanduser(args.configfile)

    if (not os.path.isfile(config_file)):
        print("ERROR: Config file does not exist: " + config_file + "\n")
    else:
        ############### READ CONFIG FILE ##################
        config = configparser.RawConfigParser(inline_comment_prefixes='#')
        config.optionxform = str
        config.sections()
        config.read(config_file)
        try:
            mode = config.get("modes", "mode")
            print("MODE: ->" + str(mode) + "<-")
            sub_mode = config.get("modes", "sub_mode")
            print("SUB_MODE: ->" + str(sub_mode) + "<-")
        except Exception as e:
            print("Issue getting a parameter from config file: %s" % str(e))

if __name__ == '__main__':
    init()

Config File (notice there is a tab before "mode" but spaces before "sub_mode"):

[modes]
    mode = blah       # modes: blah blah
    sub_mode = foo    # sub_mode: foo

Output:

MODE: ->blah
sub_mode = foo<-
Issue getting a parameter from config file: No option 'sub_mode' in section: 'modes'