weird behavior by argparse

argparse-foo.py

#!/usr/bin/env python
import argparse

def main():
    argParser = argparse.ArgumentParser(description='Test argparser')
    argParser.add_argument('-A', type=str, nargs=1, \
                            default='myarg', \
                            choices=['myarg', 'otherarg'], \
                            help='Select which arg to run', dest='arg')
    argVals = argParser.parse_args()
    print (argVals.arg,)

# $ ./argparse_demo.py
# ('myarg',)
# $ ./argparse_demo.py -A myarg
# (['myarg'],)
# $ ./argparse_demo.py -A otherarg
# (['otherarg'],)

if __name__ == "__main__":
    main()

Why does '-A myarg' make argVals.arg a list, while default keeps it a string?

It's because nargs will always make the result a list. If you leave nargs=1 out, it will return strings.