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

[Jach Feng]

Jach Feng 在 2023年1月22日 星期日上午11:11:22 [UTC+8] 的信中寫道：
> 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!? 
> 
> --Jach
I have to admit that I don't know the background upon which the argparse was built. The good side is that I don't carry its historical knowledge ( or burden?), that's why I can use it in a new way which may make someone feel uneasy.

The reason I am still keep on using argparse on this "one positional argument only" CLI app is that I can't see what advantage I can get when writing code to handling sys.argv directly for the following two situations,
-----
e:\Works\Python>py infix2postfix.py
usage: infix2postfix.py [-h] infix
infix2postfix.py: error: the following arguments are required: infix

e:\Works\Python>py infix2postfix.py -h
usage: infix2postfix.py [-h] infix

Convert infix notation to postfix

positional arguments:
  infix       Put equations in quote if there is space in it and separate each one with a comma, ie.
              "-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)))"

optional arguments:
  -h, --help  show this help message and exit
-----

comparing with code using the argparse below,

import argparse
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', 
help='Put equations in quote if there is space in it and separate each one with a comma, ie. "{}"'.format(sample))

import sys
if len(sys.argv) > 1 and not '-h' in sys.argv:
....sys.argv.insert(1, '--')
args = parser.parse_args()