How can I have an aribtrary choice using python argparse?

Question

I’m using argparse, and I’m trying to use choice to limit the options.

For the accepted values, I am looking for the input in the format of: NUMBERkm, NUMBERm, NUMBERcm. For example: 3493cm. I don’t care what the number is as long as it ends with a km,cm, or m.

I’ve tried:

parser.add_argument('-d','--distance',
                    choice=['*m','*km','*cm'])

That didn’t work.

As part of my efforts to learn python, I decided to write a small unit conversion script that takes input from arguments.

Asked By: G Derber

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Source

Answer 1

choices can’t be used this way. The test that argparse uses is

astr in choices

That matches strings in a list, tuple, keys of dictionary. A specialized class could match with a * pattern, but that’s more advanced.

An alternative to choices is to write a custom type function. Or apply that function to the value after parsing.

Your first task is to come up with a function that tests whether a string meets your criteria

def mytest(astr):
    if astr ...:
        return astr
    else:
        raise ValueError('your message')

After parsing run

mytest(args.distance)

Once you get that testing working we can talk about including it in the parser.

Answered By: hpaulj

How can I have an aribtrary choice using python argparse?

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