MIT Pset6 handSubsets v.2

def getCombinations(sortSub, size):
    """returns list with all ordered combinations of len(size)
    see itertools in python documation for more info"""
    # Note: itertools returns a tuple. Tuple not returned here
    # b/c yield function is not used
    combinations = []
    # Create tuple holding all letters of sortSub
    pool = tuple(sortSub)

    n = len(pool)

    # do nothing if len(pool) is less than the length of how long you
    # want the return tuples
    if size > n:
        return

    indices = range(size)
##    # Put first combo into list
##    # This doesn't have to be outside the while loop...
##    newCombo = ""
##    for x in indices:
##        newCombo += pool[x]
##    combinations.append(newCombo)
##    newCombo = ""
    while True:
        # add string to combinations
        # don't know why this was outside the while loop in the
        # itertools.combinations code
        newCombo = ""
        for x in indices:
            newCombo += pool[x]
        combinations.append(newCombo)
        for i in reversed(range(size)):
            # loop does not iterate i until indices[i] == i + n - size
            # I.e., the last index increases until it will index the last
            # element of pool of length n. Then, the next to last index
            # will increase in a similar fashion, until it is 1 less
            # than the index that comes after it
            # NOTE: if this loop hits break, the next time it runs it will
            # start at the beginning
            print 'i =',i,'. indices =',indices,'. Length =',n,'. Iterate i when indices[',i,'] ==,',i + n - size
            if indices[i] != i + n - size:
                print "Breaking out of loop. i starts over at",size - 1,"after rest of code runs."
                break
            print 'Iterating i!!!'

        # else: belongs to for loop, e.g., runs when for loop terminates
        # but NOT after for loop hits break
        else:
            return combinations

        # although for loop hit break, i is still in play
        # indices[i] += 1 iterates last indice in set until
        # indices[i] == i + n - size
        indices[i] += 1

        # For loop entered only when i < max(reversed(range(size)))
        # e.g., after first for loop iterates i
        # after first loop iterates, the next to last value in indices
        # also iterates after indices[i] += 1 above
        for j in range(i+1, size):
            # range(2,3) == [2]; range(3,4) == [3]; range(3,5) == [3,4]
            # last value in indices that increased as far as it could
            # is reset to one more than the the value next to it
            print 'i+1 =',i+1,"size =",size,"range(i+1, size)=",range(i+1, size),"indices =",indices
            print 'changing',indices,'to...'
            indices[j] = indices[j-1] + 1
            print indices

def combinations(iterable, r):
    # combinations('ABCD', 2) --> AB AC AD BC BD CD
    # combinations(range(4), 3) --> 012 013 023 123
    pool = tuple(iterable)
    n = len(pool)
    if r > n:
        return
    indices = range(r)
    print "indices1 range:",range(r)
    yield tuple(pool[i] for i in indices)
    while True:
        for i in reversed(range(r)):
            print "Top: i =", i,". n =", n,". r =",r,"indices =",indices
            print "If/break: indices[i] =",indices[i],". i + n - r =", i+n-r
            if indices[i] != i + n - r:
                print "break out"
                break
        else:
            print "returning"
            return
        indices[i] += 1
        print "Added: indices[i] += 1:",indices,"where i =",i
        print "entering for loop. range(i+1, r) =",range(i+1,r),"where i+1=",i+1,"and r =",r
        for j in range(i+1, r):
            print "for loop:"
            print "j =",j,". indices =",indices,". indices[j] =",indices[j],". indices[j-1] + 1 =",indices[j-1] +1
            indices[j] = indices[j-1] + 1
            print "new indices[j] =",indices[j],". indices =",indices
        yield tuple(pool[i] for i in indices)


if __name__ == '__main__':
    test = "werlkj5"
    print "I will perform the test on,",test,", with size 3!"
    testSort = getCombinations(test, 3)
    print "Result:",testSort
    print "I will try with itertools.combinations:"
    iterList = []
    for i in itertools.combinations(test, 3):
        newCombo = ""
        for x in i:
            newCombo += x
        iterList.append(newCombo)
    print iterList
##    print "I will try with combinations 'Equivalent to:' code:"
##    iterList = []
##    for i in combinations(test, 3):
##        newCombo = ""
##        for x in i:
##            newCombo += x
##        iterList.append(newCombo)
##    print iterList