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

[Weatherby,Gerard]

Argparse is for parsing command line arguments and options.

If you just want to evaluate an Python expression, use eval( )

Your string isn’t valid Python due to order of operations, but -(4^2)+5.3*abs(-2-1)/2 is.

From: Python-list <python-list-bounces+gweatherby=uchc.edu at python.org> on behalf of Jach Feng <jfong at ms4.hinet.net>
Date: Sunday, January 22, 2023 at 11:24 AM
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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Thomas Passin 在 2023年1月22日 星期日下午1:30:39 [UTC+8] 的信中寫道：
> On 1/21/2023 10:11 PM, Jach Feng wrote:
> > Fail on command line,
> >
> > e:\Works\Python>py infix2postfix.py "-4^2+5.3*abs(-2-1)/2"
> > usage: infix2postfix.py [-h] [infix]
> > infix2postfix.py: error: unrecognized arguments: -4^2+5.3*abs(-2-1)/2
> >
> > Also fail in REPL,
> >
> > e:\Works\Python>py
> > Python 3.8.8 (tags/v3.8.8:024d805, Feb 19 2021, 13:08:11) [MSC v.1928 32 bit (Intel)] on win32
> > Type "help", "copyright", "credits" or "license" for more information.
> >>>> import argparse
> >>>> parser = argparse.ArgumentParser(description='Convert infix notation to postfix')
> >>>> parser.parse_args("-4^2+5.3*abs(-2-1)/2")
> > usage: [-h]
> > : error: unrecognized arguments: - 4 ^ 2 + 5 . 3 * a b s ( - 2 - 1 ) / 2
> >
> > Just can't figure out where is wrong!?
> It just doesn't work like that. If you download the package, there is
> only one python file, __init__.py. This file contains one class. It
> has a demo at the end, commented out. If you uncomment those lines and
> run the file, you get a result printed.
>
> These remarks are based on downloading the link for the source
> distribution from Pypi
> (https://urldefense.com/v3/__https://pypi.org/project/infix2postfix/__;!!Cn_UX_p3!gqKmYLlyUndAzxmJsqCB429izQ-2-KMbpGP2eVzp_iDKtbgQXfrCu21UBvepq-F9EXb4SJwP516MHeUFMBtW$ ). When I installed it with
> pip, nothing seems to have gotten installed although pip went through
> the motions and claimed it was. So I just downloaded the source package.
>
> The test expression is "-(a*b)+(c+d)-(a+b+c+d)". The test output for
> this is "ab*-cd++ab+c+d+-".
>
> If you substitute your expression, the result is
>
> abs1-2-*2/3.5+2^4-
>
> This may or may not be correct. I'm not sure but I think it's as
> intended except for reversing "3.5". But maybe that's right, I'm not
> too sure. Notice that this file is in its first release, version 0.0.1
> - the metadata that says it's 'Development Status :: 5 -
> Production/Stable' seems to be bogus. So it may very well be buggy.
>
> At any rate, if you want to use it in a program that can accept
> arguments, you will have to write that part yourself. And the
> expression you feed it would need to be a single string, meaning it has
> to be quoted on the command line as you have done (although on Windows
> you should be using double quotes instead of single quotes).
>
> As for argparse, it isn't doing what you want because you haven't told
> it what to do with the arguments.
Sorry to cause confusion here. I don't know there is a Pypi project with the same name infix2postfix.py:-(

Nevertheless, Is there anyway to make parse_args works?
>>> parser.parse_args("-4^2+5.3*abs(-2-1)/2")
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