How to add optional arguments with default values in Python using argparse? - python-3.x

Question

I need to rewrite an arguments parser.The application has two modes: console and graphics. We can choose only one mode. Lately, the console version received two arguments: name of file with text and name of file with words. It looked so:
def parse_args():
parser = argparse.ArgumentParser(description='Fuzzy search in text')
parser.add_argument('-g', '--graphics', help='graphical version',
action='store_true')
parser.add_argument('-c', '--console', help='console version', nargs=2,
type=argparse.FileType('r'),
metavar=('TEXTFILE', 'WORDSFILE'))
return parser.parse_args()
usage: fuzzy_search.py [-h] [-g] [-c TEXTFILE WORDSFILE]
Fuzzy search in text
optional arguments:
-h, --help show this help message and exit
-g, --graphics graphical version
-c TEXTFILE WORDSFILE, --console TEXTFILE WORDSFILE
console version
Now I need to rewrite the accepting of arguments in the console version. I want to add two optional arguments that will store true for register-sensitivity (-r) and special view(-v). I know how to do it but I can't understand what to do with the next thing. I want to make two variants: 1)obligatory two files with text and words like it was initially and 2) obligatory file with text and not obligatory file with words, if it's not written than default - sys.stdin. Graphics shouldn't accept any arguments. So it should look like this
usage: fuzzy_search.py [-h] [-g] [-c [-r] [-v] TEXTFILE WORDSFILE(if not written then sys.stdin)]
I tried this variant:
parser = argparse.ArgumentParser()
subparsers = parser.add_subparsers(help='versions')
parser_console = subparsers.add_parser('console', help='console version')
parser_console.add_argument('-r', '--register-check', action='store_true', help='register sensitivity')
parser_console.add_argument('-v', '--row-view', action='store_true', help='row view')
parser_console.add_argument('TEXTFILE', type=argparse.FileType('r'), help='text file')
parser_console.add_argument('--WORDSFILE', type=argparse.FileType('r'), default=sys.stdin, help='words file')
parser_graphics = subparsers.add_parser('graphics', help='graphics version')
But when I tried this
print(parser.parse_args(['console', '-r', '-v', 'text.txt','words.txt']))
there was an error:
unrecognized arguments: words.txt
with this
print(parser.parse_args(['console', '-r', '-v', 'text.txt']))
everything is ok:
Namespace(TEXTFILE=<_io.TextIOWrapper name='text.txt' mode='r' encoding='cp1251'>, WORDSFILE=<_io.TextIOWrapper name='<stdin>' mode='r' encoding='UTF-8'>, register_check=True, row_view=True)
So problem somewhere in optional argument WORDSFILE and its default value. How to correct it?

Answer 1

Use -t for text and -w for the words file. The latter with default:
import argparse
parser = argparse.ArgumentParser()
subparsers = parser.add_subparsers(help='versions')
parser_console = subparsers.add_parser('console',
help='console version')
parser_console.add_argument('-r', '--register-check',
action='store_true', help='register sensitivity')
parser_console.add_argument('-v', '--row-view',
action='store_true', help='row view')
parser_console.add_argument('-t', '--textfile',
type=argparse.FileType('r'),
help='text file')
parser_console.add_argument('-w', '--wordsfile', type=argparse.FileType('r'),
default=sys.stdin, help='words file')
print(parser.parse_args(['console', '-r', '-v', '-t', 'text.txt',
'-w', 'words.txt']))
parser.parse_args(['console', '-r', '-v', '-t', 'text.txt'])
Output:
Namespace(register_check=True, row_view=True,
textfile=<_io.TextIOWrapper name='text.txt' mode='r' encoding='UTF-8'>,
wordsfile=<_io.TextIOWrapper name='words.txt' mode='r' encoding='UTF-8'>)
Namespace(register_check=True, row_view=True,
textfile=<_io.TextIOWrapper name='text.txt' mode='r' encoding='UTF-8'>,
wordsfile=<_io.TextIOWrapper name='<stdin>' mode='r' encoding='UTF-8'>)