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

Solution 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.

Solution 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.

Solution 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

Comments

[m77r44]

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

[SilentGhost]

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

[Glenn Maynard]

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...

[Pure Jobs Inc.]

@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.

[SilentGhost]

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

[user1750701]

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.

[user1750701]

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

[Pure Jobs Inc.]

@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.

[Alexej Magura]

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