How to make argparse accept "-4^2+5.3*abs(-2-1)/2" string argument?

[Weatherby,Gerard]

Use a different prefix character

    parser = argparse.ArgumentParser(prefix_chars='%')
    parser.add_argument('expression')

    args = parser.parse_args()
    print(args.expression)

argparser is for allowing multiple command line options to be passed, providing default, controlling the number of arguments and the like.


From: Python-list <python-list-bounces+gweatherby=uchc.edu at python.org> on behalf of Jach Feng <jfong at ms4.hinet.net>
Date: Wednesday, January 25, 2023 at 12:25 PM
To: python-list at python.org <python-list at python.org>
Subject: Re: How to make argparse accept "-4^2+5.3*abs(-2-1)/2" string argument?
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Chris Angelico 在 2023年1月25日 星期三下午1:16:25 [UTC+8] 的信中寫道：
> On Wed, 25 Jan 2023 at 14:42, Jach Feng <jf... at ms4.hinet.net> wrote:
> > I was happy working with argparse during implement my script. To save the typing, I used a default equation for testing.
> >
> > sample = "-4^2+5.3*abs(-2-1)/2, abs(Abc)*(B+C)/D, (-3) * sqrt(1-(x1/7)*(y1/7)) * sqrt(abs((x0-4.5)/(y0-4)))"
> > parser = argparse.ArgumentParser(description='Convert infix notation to postfix')
> > parser.add_argument('infix', nargs='?', default=sample, help="....")
> >
> You're still not really using argparse as an argument parser. Why not
> just do your own -h checking? Stop trying to use argparse for what
> it's not designed for, and then wondering why it isn't doing what you
> expect it to magically know.
>
> ChrisA
I just don't get what you mean?

> You're still not really using argparse as an argument parser. Why not just do your own -h checking?

Is a math equation not qualified as a command line "argument"? What criteria do you use when judging the quality of an "argument"?

> Stop trying to use argparse for what it's not designed for,

Even the author considers a positional argument begin with '-' is a legal argument. Below is a quote from its manual.

"If you have positional arguments that must begin with - and don’t look like negative numbers, you can insert the pseudo-argument '--' which tells parse_args() that everything after that is a positional argument"

> and then wondering why it isn't doing what you expect it to magically know."

I don't expect magic, I expect the consistency of a parser.
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