On 25Jan2023 16:15, Chris Angelico <rosuav at gmail.com> wrote:
>On Wed, 25 Jan 2023 at 14:42, Jach Feng <jfong 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.
Sure, but what benefit was it bringing you? Just the usage (help)
message? Did you have many options to handle?
>> 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="....")
If this was the whole thing, I don't see what argparse was doing for you
which was better than just handling the arguments yourself - there's
only one after all.
>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.
I'm with Chris here.
As someone who pretty well _never_ uses argparse, and occasionally uses
getopt, I'd do something like this:
usage = '''Usage: infix
Parse the argument infix as an expression, print the result.'''
badopts = False
cmd = argv.pop(0)
if not argv:
print(f'{cmd}: missing infix argument', file=sys.stderr)
badopts = True
else:
infix = argv.pop(0)
if infix in ('-h', '--help'):
print(usage)
exit(0)
if argv:
print(f'{cmd}: extra arguments after infix: {argv!r}', file=sys.stderr)
badopts = True
if badopts:
print(usage, file=sys.stderr)
exit(2)
... work with infix as desired ...
This:
- avoids trying to shoehorn argparse into behaving in a way it was not
designed for
- avoids users needing to know the standard UNIX/POSIX "--" idiom for
marking off the end of options
- supports a -h or --help leading option
Cheers,
Cameron Simpson <cs at cskk.id.au>