Here is an evil imperative, non-recursive generator:
def ncsub(seq):
n = len(seq)
R = xrange(n+1)
for i in xrange(1,2**n):
S = []
nc = False
for j in R:
k = i>>j
if k == 0:
if nc:
yield S
break
elif k%2 == 1:
S.append(seq[j])
elif S:
nc = True
And here is a cython version without yield expression which won't work
with cython:
def ncsub(seq):
n = len(seq)
cdef int i,j,k,nc
res = []
R = xrange(n+1)
for i in xrange(1,2**n):
S = []
nc = False
for j in R:
k = i>>j
if k == 0:
if nc:
res.append(S)
break
elif k%2 == 1:
S.append(seq[j])
elif S:
nc = True
return res
Application: list(ncsub(range(19)))
On my 1.5GHz notebook your original version needed 11.2s ( psyco
version = 9.5s), my pure Python generator got it in 7.75s and the
cython version in 2.3s.
[Yes, I have too much time...]
--
http://mail.python.org/mailman/listinfo/python-list
