I want to create argument parser with following signature:
./myapp [-a [-b BVAL] | -c]
In other words, user could provide argument -b BVAL only in case if he provided argument -a.
It's quite easy to create mutually exclusive group of -a and -c, but I can't figure out how to create relationship allow -b only if -a provided
You could inherit from ArgumentParser to add some custom functionality. Here I am raising an exception, but you could modify this to implement whatever you would like. Just change the on_dependency_error() method to suit your needs.
from argparse import ArgumentParser
class FancyParser(ArgumentParser):
# {'b': 'a'} Where b depends on a
dependencies = {}
def on_dependency_error(self, arg, depends_on):
raise FancyParser.DependencyError(
'Argument %s depends on %s' % (arg, depends_on))
def add_argument(self, *args, **kwargs):
depends_on = kwargs.get('depends_on')
if depends_on:
self.dependencies[kwargs.get('dest') or args[0]] = depends_on
del kwargs['depends_on']
return super(FancyParser, self).add_argument(*args, **kwargs)
def parse_args(self, *args, **kwargs):
args = super(FancyParser, self).parse_args(*args, **kwargs)
for arg, depends_on in self.dependencies.iteritems():
if getattr(args, arg) and not getattr(args, depends_on):
self.on_dependency_error(arg, depends_on)
return args
class DependencyError(Exception):
def __init__(self, *args, **kwargs):
return super(FancyParser.DependencyError,
self).__init__(*args, **kwargs)
You can then use it like this -
args = ['-a', '-b', 'BVAL', '-c']
parser = FancyParser()
parser.add_argument('-a', dest='a', action='store_true')
parser.add_argument('-b', dest='b', depends_on='a')
parser.add_argument('-c', dest='c', action='store_true')
try:
parser.parse_args(args)
except FancyParser.DependencyError as e:
# Whatever here...
pass
parse_args() method to better test for dependency. You'll want to use the updated code. Thanks!Docopt does it just as I wanted. Terrific!
docopt('./myapp [-a [-b BVAL] | -c]')
It's not exactly what you're looking for but maybe what you could use add_subparsers() (doc)?
Do something like:
import argparse
parser = argparse.ArgumentParser()
subparsers = parser.add_subparsers(help='sub-command help')
a = subparsers.add_parser('a')
c = subparsers.add_parser('c')
a.add_argument('b')
If you don't want to use subparsers, you can handle your argument values yourself using parser.error.
import argparse
parser = argparse.ArgumentParser()
parser.add_argument('-a', dest='a', default='') # you can use other defaults surely
parser.add_argument('-b', dest='b', default='')
parser.add_argument('-c', dest='c', default='')
args = parser.parse_args()
if args.b and not args.a:
parser.error("Option 'b' can't be specified without 'a'")
But still consider using subparsers in case you might extend the logic
