CODEWITHSUNDEEP
pythonpython-3.xcommand-line-argumentsargparse
Fabian Henze
Fabian Henze

Reputation: 1007

argparse: dependency between multiple optional positional arguments

I am looking for a way to parse the following commandline syntax using the argparse module in python3:

myapp.py [folder] [[from] to]

Meaning: The user may optionally define a folder, which defaults to cwd. Additionally the user may pass up to two integers. If only one number is given, it should be stored in the to variable. This is similar to the syntax of the python builtin range().

e.g.:

myapp.py folder
myapp.py 10
myapp.py 5 10
myapp.py folder 5 10
myapp.py folder 10

Is that possible? If so, how?

Upvotes: 2

Views: 1571

Answers (4)

David
David

Reputation: 6571

I couldn't see a way to do it without using a named argument for folder:

# usage: argparsetest2.py [-h] [--folder [FOLDER]] [to] [fr]

import argparse
import os

parser = argparse.ArgumentParser()
parser.add_argument('--folder', dest='folder', nargs='?', default=os.getcwd())
parser.add_argument('to', type=int, nargs='?')
parser.add_argument('fr', type=int, nargs='?')
args = parser.parse_args()

print args

Upvotes: 0

user1277476
user1277476

Reputation: 2909

I'd also suggest parsing sys.argv yourself.

FWIW, I parse sys.argv even on projects where argparse or similar would work, because parsing sys.argv yourself plays nicely with pylint or flake8.

Upvotes: 0

mgilson
mgilson

Reputation: 309891

You can do something quite silly:

import argparse
import os

class MyAction(argparse.Action):
    def __call__(self,parser,namespace,values,option_string=None):
        namespace.numbers = []
        namespace.path = os.getcwd()
        for v in values:
            if os.path.isdir(v):
                namespace.path = v
            else:
                try:
                    namespace.numbers.append(int(v))
                    if len(namespace.numbers) > 2
                       parser.error("Barg2!!!")
                except ValueError:
                    parser.error("Barg!!!")

p = argparse.ArgumentParser()
p.add_argument('stuff',nargs='*',action=MyAction)
n = p.parse_args()
print n

But if you're going to do this, you might as well just process sys.argv yourself -- you should really consider using actual options here...

Upvotes: 1

nneonneo
nneonneo

Reputation: 179392

Use options; that's what they're there for (and what argparse is good at parsing).

Thus, a syntax like

myapp.py [-F folder] [[from] to]

would make a lot more sense, and be easier to parse.

Upvotes: 1

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