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pythonargparse
Nick Falco
Nick Falco

Reputation: 207

Python argparse with -- as the value

Is there a way to pass -- as a value to a Python program using argparse without using the equals (=) sign?

The command line arguments that I added to the argparser are defined like below:

parser.add_argument('--myarg', help="my arg description")

You would use this argument in a program like this:

python myprogram.py --myarg value123

Is there a way to run this program with -- as the value instead of 'value123'?

i.e

python myprogram.py --myarg --

Upvotes: 5

Views: 6198

Answers (3)

René
René

Reputation: 354

Tested in Python 3.8:

Using the equal sign and quotes around the values definitely solves that issue:

--myarg="--"

Upvotes: -1

roipoussiere
roipoussiere

Reputation: 5946

I had the same problem and found this hacky one-liner which modifies sys.argv:

import sys, argparse

sys.argv = [ ('__' if arg == '--' else arg) for arg in sys.argv ]

parser = argparse.ArgumentParser(description='A simple test')
parser.add_argument('path', help='Path of file (use `--` to read from stdin)')
args = parser.parse_args()

print('input is', 'stdin' if args.path == '__' else args.path)

Output:

> python test.py --
input is stdin
> python test.py foo.bar
input is foo.bar

Upvotes: 0

wim
wim

Reputation: 362557

I suspect it will not be possible to make argparse do this natively. You could pre-process sys.argv though, as a non-intrusive workaround. 

import sys
from argparse import ArgumentParser
from uuid import uuid4

sentinel = uuid4().hex

def preprocess(argv):
    return [sentinel if arg == '--' else arg for arg in argv[1:]]

def postprocess(arg):
    return '--' if arg == sentinel else arg

parser = ArgumentParser()
parser.add_argument('--myarg', help="my arg description", type=postprocess)
args = parser.parse_args(preprocess(sys.argv))

Upvotes: 4

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