[Python-Dev] PEP 389: argparse - new command line parsing module (original) (raw)

"Martin v. Löwis" martin at v.loewis.de
Tue Sep 29 05:44:30 CEST 2009

Let's take getopt.getopt(sys.argv[1:], "a:b", ["alpha=", "beta"]) as an example and simply assume that 'alpha' takes a string as an argument and that it's required and that 'beta' is a boolean flag. To pull everything out you could do::

options, args = getopt.getopt(sys.argv[1:], "a:b", ["alpha=", "beta"]) optionsdict = dict(options) alpha = optionsdict.get('-a', optionsdict.get('--alpha', '')) beta = '-b' in optionsdict or '--beta' in optionsdict main(alpha, beta, args) Obviously if one of the getopt supporters has a better way of doing this then please speak up.

As Yuvgoog Greenle says, the canonical getopt way is to write

alpha = None beta = False options, args = getopt.getopt(sys.argv[1:],"a:b",['alpha=','beta']): for opt, val in options: if arg in ('-a','--alpha'): alpha = val elif arg in ('-b','--beta'): beta = True main(alpha, beta, args)

Even though this is many more lines, I prefer it over optparse/argparse: this code has only a single function call, whereas the argparse version has three function calls to remember. The actual processing uses standard Python data structures which I don't need to look up in the documentation.

Now, Steven, can you show how best to do this in argparse?

This demonstrates my point: you were able to use getopt right away (even though not in the traditional way), whereas you need to ask for help on using argparse properly.

I am willing to bet that the total number of lines to do this is not that much more and does not require you to know to use 'or' or the dict constructor along with dict.get() in order to keep it compact.

See above - getopt users don't care about compactness in the processing.

I can only imagine what some newbie might try to do in order to be correct (if they even try).

Depends on the background of the newbie. If they come from C, they immediately recognize the way of doing things.

Regards, Martin

More information about the Python-Dev mailing list