Development of Creative Commons licenses

[Mike Linksvayer <ml AT creativecommons.org>]

cc-relicense.py attached

Comments on accuracy desired.  Even if you can't read python you can 
read the rules as explained in comments.

Eventually we may make this available as a web service so people can 
build Flash toys or whatever to help people visualize how licenses combine.

--
  Mike Linksvayer
  http://creativecommons.org/about/people#21
# encodes rules for relicensing Creative Commons licensed works
#
# relicense() function contains the logic
#
# combine() accepts multiple licenses, calls relicense() for
# each and returns intersection of allowable licenses
#
# see tests at end for expected values
#
# read comments in relicense() for explanation of rules

import copy

DEBUG = 0
LICENSES = 
['by','by-nc','by-nc-nd','by-nc-sa','by-nd','by-sa','nc-sampling+','publicdomain','sampling','sampling+']

def debug(msg):
    if (DEBUG):
        print msg

# keep only licenses matching 'keep' parameter
def keep(licenses, keep):
    for license in copy.copy(licenses):
        if (license.find(keep) == -1):
            licenses.remove(license)
            debug('keep: '+keep+' REMOVED: '+license)
        else:
            debug('keep: '+keep+' KEPT: '+license)

# remove licenses matching 'remove' parameter
def remove(licenses, remove):
    for license in copy.copy(licenses):
        if (license.find(remove) != -1):
            licenses.remove(license)
            debug('remove: '+remove+' REMOVED: '+license)
        else:
            debug('remove: '+remove+' KEPT: '+license)

# allowed relicensing options for a single license
def relicense(license):
    relicenses = copy.copy(LICENSES)
    # PD allows anything
    if (license.find('publicdomain') != -1):
        return relicenses
    # sampling requires attribution although 'by' isn't in the URI
    if (license.find('by') != -1 or license.find('sampling') != -1):
        remove(relicenses,'publicdomain')
    # noncommercial must be propagated
    if (license.find('nc') != -1):
        keep(relicenses,'nc')
    # noderivs must be propagated.  note that this is only good for
    # redistribution of verbatim copies, does not allow derivative works
    if (license.find('nd') != -1):
        keep(relicenses,'nd')
    # sharealike requires exact license match
    if (license.find('sa') != -1 and license.find('sampling') == -1):
        keep(relicenses,license)
    # sampling requires another sampling license to propagate
    # no advertising and transformation requirement
    # unadorned sampling requires unadorned sampling to propagate
    # no verbatim distribution
    if (license.find('sampling') != -1):
        keep(relicenses, 'sampling')
        if (license.find('sampling+') == -1):
            remove(relicenses,'sampling+')
    return relicenses

# intersection of allowed relicensing options for each license
def combine(licenses):
    relicenseset = None
    for license in licenses:
        thisrelicenseset = set(relicense(license))
        if (relicenseset == None):
            relicenseset = thisrelicenseset
        else:
            relicenseset = relicenseset.intersection(thisrelicenseset)
    return relicenseset

def test(license, expectedrelicenses):
    if (isinstance(expectedrelicenses,set)):
        relicenses = combine(license)
    else:
        relicenses = relicense(license)
    if (relicenses == expectedrelicenses):
        print 'PASS:', license, 'expected&got:', relicenses
    else:
        print 'FAIL:', license, 'expected:', expectedrelicenses, 'expected:', 
relicenses

# test each license against expected values
test('by',['by','by-nc','by-nc-nd','by-nc-sa','by-nd','by-sa','nc-sampling+','sampling','sampling+'])
test('by-nc',['by-nc','by-nc-nd','by-nc-sa','nc-sampling+'])
test('by-nc-nd',['by-nc-nd'])
test('by-nc-sa',['by-nc-sa'])
test('by-nd',['by-nc-nd','by-nd'])
test('by-sa',['by-sa'])
test('nc-sampling+',['nc-sampling+'])
test('publicdomain',LICENSES)
test('sampling',['sampling'])
test('sampling+',['nc-sampling+','sampling','sampling+'])

# test just a few multi-license combinations
test(['by-nc-sa','nc-sampling+'],set([]))
test(['by-sa','by-nc-sa'],set([]))
test(['by','publicdomain','sampling+'],set(['nc-sampling+','sampling','sampling+']))