avi.e...@gmail.com 在 2023年1月25日 星期三清晨6:39:13 [UTC+8] 的信中寫道：
> If I understood the issue, the problem is the unary minus at the start of the
> expression.
>
> So if you know the expression is in that argument, would it make sense to pad
> it in one of many ways that are otherwise harmless?
>
> Could you put parens on both sides of "-4^2+5.3*abs(-2-1)/2":
>
> "(-4^2+5.3*abs(-2-1)/2)"
>
> Or perhaps place a zero in front as in the awkward case where it begins with
> a minus sign:
>
> "0 -4^2+5.3*abs(-2-1)/2"
>
> Some people suggest you ask the user to modify what they type in and such
> changes may work. Your program could also potentially diddle with argv and
> recognize it albeit as you allow calling a function like abs() I can easily
> imagine a potentially valid looking "-abs(...)..." that could look like -a
> followed by something.
>
> I see a deeper issue with interactions at the command shell level if parts of
> the arithmetic expression are evaluated or changed before python is even
> invoked.
>
> Then again, I may be misunderstanding the issue.
> -----Original Message-----
> From: Python-list <python-list-bounces+avi.e.gross=gmai...@python.org> On
> Behalf Of Jach Feng
> Sent: Tuesday, January 24, 2023 2:21 AM
> To: pytho...@python.org
> Subject: Re: How to make argparse accept "-4^2+5.3*abs(-2-1)/2" string
> argument?
> cameron...@gmail.com 在 2023年1月24日 星期二下午2:05:33 [UTC+8] 的信中寫道：
> > On 23Jan2023 17:58, Jach Feng <jf...@ms4.hinet.net> wrote:
> > >>>> parser.parse_args(['--', 'infix2postfix.py', '-4.3+5'])
> > >usage: [-h] infix
> > >: error: unrecognized arguments: -4.3+5
> > This error doesn't look like "-4.3+5 looks like an option" but instead
> > "we don't expect any arguments after "infix".
> >
> > Not personally a fan of argparse myself, but then I have my own
> > elaborate command line framework which generally uses getopt for the
> > option stuff.
> >
> > Cheers,
> > Cameron Simpson <c...@cskk.id.au>
> Hmm, good to you. During experiments in these days, I had found argparse
> shows some strange/unstable behaviors in dealing with the leading '-'
> situation.
> --
> https://mail.python.org/mailman/listinfo/python-list
The user may not know any unix idiom, or even don't know Python. Ask them to
add extra characters in their equations to avoid the argparse conflict is
strange to me.
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