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
OK, I take a quick try to use argv directly. I write the code in a way even get rid of the -h option.

import sys
if len(sys.argv) == 1:
....infix = " "
....print("Usage: a math equation must follow!")
else:
....infix = "".join(sys.argv[1:])

Simple enough, right? But unfortunately it didn't survive. The ^ symbol was lost!

e:\Works\Python>py infix2postfix.py
Usage: a math equation must follow!

e:\Works\Python>py infix2postfix.py -4^2 +5.3  *  abs(-2-1)/2
-42 5.3 -2 1 - abs * 2 / +

Hmm...