Is there anyway to persuade python's getopt to handle optional parameters to options?

Question

According to the documentation on python's getopt (I think) the options fields should behave as the getopt() function. However I can't seem to enable optional parameters to my code:

#!/usr/bin/python
import sys,getopt

if __name__ == "__main__":
    try:
        opts, args = getopt.gnu_getopt(sys.argv[1:], "v::", ["verbose="])
    except getopt.GetoptError, err:
        print str(err)
        sys.exit(1)

    for o,a in opts:
        if o in ("-v", "--verbose"):
            if a:
                verbose=int(a)
            else:
                verbose=1
            print "verbosity is %d" % (verbose)

Results in:

$ ./testopt.py -v
option -v requires argument
$ ./testopt.py -v 1
verbosity is 1

Misstate

Answer 1

getopt doesn't support optional parameters. in case of long option you could do:

$ ./testopt.py --verbose=

which will result in empty-string value.

You could find argparse module to be more flexible. This replaces the older optparse module.

Papeete

Answer 2

Unfortunately, there is no way. From the optparse docs:

Typically, a given option either takes an argument or it doesn’t. Lots of people want an “optional option arguments” feature, meaning that some options will take an argument if they see it, and won’t if they don’t. This is somewhat controversial, because it makes parsing ambiguous: if "-a" takes an optional argument and "-b" is another option entirely, how do we interpret "-ab"? Because of this ambiguity, optparse does not support this feature.

EDIT: oops, that is for the optparse module not the getopt module, but the reasoning why neither module has "optional option arguments" is the same for both.

Winnow

Yeah I just noticed that, classic case of "wrong tab" syndrome. However, I still think this reasoning is relative for getopt too. – Winnow

Also, long options can have optional arguments unambiguously; "--foo" vs. "--foo=arg". Python's doesn't appear to support this, which is very poor; a symptom of halfway reimplementing something from scratch... – Pineda

@Glenn: python supports everything, maintainer of optparse doesn't. See my answer for decent module. – Papeete

I had read the optparse docs describing why they didn't support the feature but it wasn't clear for opt. It's a shame as -v or -v 2 is a fairly useful idiom which both perl and C have no problem with. – Misstate

Answer 3

You can do an optional parameter with getopt like this:

import getopt
import sys

longopts, shortopts = getopt.getopt(sys.argv[1:], shortopts='', longopts=['env='])
argDict = dict(longopts)

if argDict.has_key('--env') and argDict['--env'] == 'prod':
    print "production"
else:
    print "sandbox"

Usage:

$ python scratch.py --env=prod
production

$ python scratch.py --env=dev
sandbox

$ python scratch.py
sandbox

Meir

Except your example doesn't show you using optional arguments: will --env still work without an accompanying argument? – Heredes

Answer 4

If you're using version 2.3 or later, you may want to try the optparse module instead, as it is "more convenient, flexible, and powerful ...", as well as newer. Alas, as Pynt answered, it doesn't seem possible to get exactly what you want.

Rensselaerite

except from optparser docs was posted by Pynt 45 minutes ago! – Papeete

@SilentGhost: In my reading of Pynt's answer, I see nothing recommending optparse over get_opt, which is what I was getting at. Admittedly, I didn't explain that well originally, but have edited to do so. – Rensselaerite

optparse specifically says it does not support optional parameters to options. – Misstate

@stsquad: Yes, I noted that in the (edited) answer. My point was that you may want to consider optparse instead of get_opt if you're going to do this. – Rensselaerite

Answer 5

python's getopt should really support optional args, like GNU getopt by requiring '=' be used when specifying a parameter. Now you can simulate it quite easily though, with this constraint by implicitly changing --option to --option=

I.E. you can specify that --option requires an argument, and then adjust --option to --option= as follows:

for i, opt in enumerate(sys.argv):
    if opt == '--option':
        sys.argv[i] = '--option='
    elif opt == '--':
        break

Peaceful