python 排列组合算法

def c(n,m,out):
if(m==0):
   return 1
x=n
while x>=m:
   out.append(x)
   if(c(x-1,m-1,out)):
    print out
   out.pop()
   x-=1
return 0
c(10,8,out=[])

def permutation(listobj, length):
assert listobj != None and 0 < length <= len(listobj)
if(length == 1):
   return [ [x] for x in listobj ]
result = []
for i in range(len(listobj)):
   cp = list(listobj)
   cur = cp[i]
   del cp[i]
   result.extend( [cur] + x for x in permutation(cp, length-1) )
return result

n个取m个数的组合数问题