I am writing the script where I pass values with CLI through argparse module. I am wondering if this is possible to restrict variable to hold pre-defined values, to avoid user mistake. It is not the type restriction, values are consists of letters as well as digits, surely I can write an if block, but I have about 30 pre-defined values, so writing something like
if var is value1 or var is value2 ... or var is value30:
pass
else:
print("oops, your value does not fit")
would be painful. What is the proper way of doing this?
With choices:
In [214]: parser = argparse.ArgumentParser()
In [215]: parser.add_argument('--foo', choices=['one','two','three','four']);
Accepted:
In [216]: parser.parse_args('--foo one'.split())
Out[216]: Namespace(foo='one')
rejected:
In [217]: parser.parse_args('--foo five'.split())
usage: ipython3 [-h] [--foo {one,two,three,four}]
ipython3: error: argument --foo: invalid choice: 'five' (choose from 'one', 'two', 'three', 'four')
help:
In [218]: parser.parse_args('-h'.split())
usage: ipython3 [-h] [--foo {one,two,three,four}]
optional arguments:
-h, --help show this help message and exit
--foo {one,two,three,four}
If I'd defined a metavar, the help will be
usage: ipython3 [-h] [--foo CHOICES]
optional arguments:
-h, --help show this help message and exit
--foo CHOICES
Or if the choices is too long, define a type function:
In [222]: def mychoices(astr):
...: if astr in ['one','two','three','four']:
...: return astr
...: else:
...: raise argparse.ArgumentTypeError('Wrong choice')
In [223]: parser = argparse.ArgumentParser()
In [224]: parser.add_argument('--foo', type=mychoices);
In [225]: parser.parse_args('--foo one'.split())
Out[225]: Namespace(foo='one')
In [226]: parser.parse_args('--foo five'.split())
usage: ipython3 [-h] [--foo FOO]
ipython3: error: argument --foo: Wrong choice
In [227]: parser.parse_args('-h'.split())
usage: ipython3 [-h] [--foo FOO]
optional arguments:
-h, --help show this help message and exit
--foo FOO