Question

How can options/arguments determine which function is chosen during program execution? For the example I have two options depending on the option I would like them to use their respective functions. What am I missing?

import os, sys, glob
from optparse import OptionParser

def fname(arguments):
    files = []
    for arg in arguments:
        if '*' in arg or '?' in arg:
            # contains a wildcard character
            files.extend(glob.glob(arg))
        elif os.path.isdir(arg):
            # is a dictionary
            files.extend(glob.glob(os.path.join(arg, '*')))
        elif os.path.exists(arg):
            # is a file
            files.append(arg)
        else:
            # invalid?
            print '%s invalid' % arg
    return files

# check if file exists locally, if not: download it
def downnload(filename, keyString):
    if not os.path.exists(filename+keyString):
        l.get_contents_to_filename(filename+keyString)

# List bucket contents
def blist(bucket):
    for b in rs:
        print b.name

def main():
    usage = "usage: %prog [options] -f filename"
    parser = OptionParser(usage)
    parser.add_option('-d', '--download',
            action='store', dest='download',
            default=None, help='download files from cloud')
    parser.add_option('-l', '--list',
            action='store', dest='bucket',
            default=None, help='list buckets or contents of specified bucket')

    if len(sys.argv) == 1:
        parser.print_help()
        sys.exit()
    (options, args) = parser.parse_args()

    # from boto import
    bucket_list = bucket.list()
    for l in bucket_list:
        keyString = str(l.key)

    downnload(options.filename, keyString)
    blist(options.bucket)

if __name__ == '__main__':
    main()

Answer 1

You are missing a lot.

1. Where is filename given a value?
2. Where is keyString given a value?
3. Where is bucket given a value?
4. You shouldn’t name your function list since that it is a primitive type

You probably want to look at the optparse tutorial. I’m assuming that you expecting bucket to receive the value from the --list command line argument. The value gets stored into options.bucket instead. That is just a start.

I think that you want to change the end of main to check the options and call the appropriate function. Something like:

def main():
    # much omitted
    if options.filename is not None:
        downnload(options.filename, keyString)
    elif options.bucket is not None:
        blist(options.bucket)
    else:
        print 'Either --download or --list is required.'
        parser.print_help()
        sys.exit(-1)

I think that this is what you are looking for. It decides which function to call based on the command line arguments passed in. For example, if the user passes --download filename then the downnload function is called with the supplied filename as the argument.