How do I set up argparse as follows:
if -2 is on the command line, no other arguments are required
if -2 is not on the command line, -3 and -4 arguments are required
For example,
-2 [good]
-3 a -4 b [good]
-3 a [not good, -4 required]
-2 -5 c [good]
-2 -3 a [good]
There are a number of similar questions here, but either they don't address this situation or I don't understand.
Python 2.7 if that matters.
A subparser (as suggested in comments) might work.
Another alternative (since mutually_exclusive_group can't quite do this) is just to code it manually, as it were:
import argparse
def main():
parser = argparse.ArgumentParser()
parser.add_argument('-2', dest='two', action='store_true')
parser.add_argument('-3', dest='three')
parser.add_argument('-4', dest='four')
parser.add_argument('-5', dest='five')
args = parser.parse_args()
if not args.two:
if args.three is None or args.four is None:
parser.error('without -2, *both* -3 <a> *and* -4 <b> are required')
print args
return 0
Adding a little driver to this:
import sys
sys.exit(main())
and run with your examples, it seems to do the right thing; here are two runs:
$ python mxgroup.py -2; echo $?
Namespace(five=None, four=None, three=None, two=True)
0
$ python mxgroup.py -3 a; echo $?
usage: mxgroup.py [-h] [-2] [-3 THREE] [-4 FOUR] [-5 FIVE]
mxgroup.py: error: without -2, *both* -3 <a> *and* -4 <b> are required
2
$
parse_known_args to check for the -2 flag, and if that is missing, use another parser to look for -3 and -4.
I think it is pretty hard to achieve that (including a nice help message) while only using the standard argparse functions. You can however easily test it yourself after parsing the arguments. You can describe the extra requirements in the epilogue or so. Note that it is unusual to use numbers as options, I had to use dest='two', since args.2 is not valid syntax.
#!/usr/bin/env python
import argparse
parser = argparse.ArgumentParser(
description='bla bla',
epilog='Note: arguments -3 and -4 are required when -2 is missing')
parser.add_argument('-2', dest='two', action='store_true')
parser.add_argument('-3', dest='three')
parser.add_argument('-4', dest='four')
parser.add_argument('-5', dest='five')
args = parser.parse_args()
if not args.two and (args.three is None or args.four is None):
parser.error('arguments -3 and -4 are required when -2 is missing')
print 'Good:', args
With these results:
[~]: ./test.py -h
usage: test.py [-h] [-2] [-3 THREE] [-4 FOUR] [-5 FIVE]
bla bla
optional arguments:
-h, --help show this help message and exit
-2
-3 THREE
-4 FOUR
-5 FIVE
Note: arguments -3 and -4 are required when -2 is missing
[~]: ./test.py -2
Good: Namespace(five=None, four=None, three=None, two=True)
[~]: ./test.py -3 a -4 b
Good: Namespace(five=None, four='b', three='a', two=False)
[~]: ./test.py -3 a
usage: test.py [-h] [-2] [-3 THREE] [-4 FOUR] [-5 FIVE]
test.py: error: arguments -3 and -4 are required when -2 is missing
[~]: ./test.py -2 -5 c
Good: Namespace(five='c', four=None, three=None, two=True)
[~]: ./test.py -2 -3 a
Good: Namespace(five=None, four=None, three='a', two=True)
args.2 does not work, getattr(args,'2') does. Arguments like -2 are allowed, but add unnecessary complications.You can define parameter as optional but then you can check it later and raise an exception as below;
import argparse
TYPES = ["once", "weekly"]
DAYS = ["monday", "tuesday", "wednesday",
"thursday", "friday", "saturday", "sunday"]
def take_arg():
ap = argparse.ArgumentParser()
ap.add_argument("-t", "--type", required=True,
help="select the type {}".format(TYPES))
ap.add_argument("-d", "--day", required=False, help="write a day {}".format(DAYS))
arg = ap.parse_args()
if arg.type == "weekly":
if arg.day not in DAYS:
raise Exception("DayParamNotExist")
return arg
def main():
ap_res=take_arg()
print(ap_res)
if __name__ == '__main__':
main()
-can be tricky.-2may work, but-tor--twowouldn't because they look like optionals. But if-3is defined as an argument, then-2no longer works as a subparser command (or a choice).