Can argparse in python 2.7 be told to require a minimum of TWO arguments?
Pergunta
My application is a specialized file comparison utility and obviously it does not make sense to compare only one file, so nargs='+'
is not quite appropriate.
nargs=N
only excepts a maximum of N
arguments, but I need to accept an infinite number of arguments as long as there are at least two of them.
Solução
Short answer is you can't do that because nargs doesn't support something like '2+'.
Long answer is you can workaround that using something like this:
parser = argparse.ArgumentParser(usage='%(prog)s [-h] file file [file ...]')
parser.add_argument('file1', nargs=1, metavar='file')
parser.add_argument('file2', nargs='+', metavar='file', help=argparse.SUPPRESS)
namespace = parser.parse_args()
namespace.file = namespace.file1 + namespace.file2
The tricks that you need are:
- Use
usage
to provide you own usage string to the parser - Use
metavar
to display an argument with a different name in the help string - Use
SUPPRESS
to avoid displaying help for one of the variables - Merge two different variables just adding a new attribute to the
Namespace
object that the parser returns
The example above produces the following help string:
usage: test.py [-h] file file [file ...]
positional arguments:
file
optional arguments:
-h, --help show this help message and exit
and will still fail when less than two arguments are passed:
$ python test.py arg
usage: test.py [-h] file file [file ...]
test.py: error: too few arguments
Outras dicas
Couldn't you do something like this:
import argparse
parser = argparse.ArgumentParser(description = "Compare files")
parser.add_argument('first', help="the first file")
parser.add_argument('other', nargs='+', help="the other files")
args = parser.parse_args()
print args
When I run this with -h
I get:
usage: script.py [-h] first other [other ...]
Compare files
positional arguments:
first the first file
other the other files
optional arguments:
-h, --help show this help message and exit
When I run it with only one argument, it won't work:
usage: script.py [-h] first other [other ...]
script.py: error: too few arguments
But two or more arguments is fine. With three arguments it prints:
Namespace(first='one', other=['two', 'three'])