On 10.06.2012 23:27, Paul Rubin wrote: > Here is an exercise from the book that you might like to try in Python: > > http://mitpress.mit.edu/sicp/full-text/book/book-Z-H-24.html#%_idx_3894 > > It's not easy ;-)
I liked this exercize. At first I wrote my own merger. > def merge(*iterables): > iterables = list(iterables) > current = [i.next() for i in iterables] > last = None > while True: > m = min(current) > while last == m: > p = current.index(m) > try: > current[p] = iterables[p].next() > except StopIteration: > del current[p] > del iterables[p] > if len(current) == 0: > raise StopIteration > m = min(current) > yield m > last = m But then I realised the vast library of python already contained (a faster) one (propably based upon <http://code.activestate.com/recipes/491285-iterator-merge/>), which just needed to be enhanced a little bit to allow duplicate items to be removed: > import heapq > > def skipdups(m): > l = k = m.next() > yield k > while True: > while l == k: > k = m.next() > yield k > l = k > > def gen_s(): > s = [1] > m = skipdups(heapq.merge(*[(lambda j: (k*j for k in s))(n) for n in > [2,3,5]])) > yield s[0] > while True: > k = m.next() > s.append(k) > yield k Now gen_s() generates the wanted sequence. Greetings -- http://mail.python.org/mailman/listinfo/python-list
