方式1：
#!/usr/bin/env python
#-*- encoding: utf-8 -*-
def permutations(iterable, r=None):
# permutations(‘ABCD‘, 2) --> AB AC AD BA BC BD CA CB CD DA DB DC
# permutations(range(3)) --> 012 021 102 120 201 210
pool = tuple(iterable)
n = len(pool)
r = n if r is None else r
if r > n:
return
indices = range(n)
cycles = range(n, n-r, -1)
yield tuple(pool[i] for i in indices[:r])
while n:
for i in reversed(range(r)):
cycles[i] -= 1
if cycles[i] == 0:
indices[i:] = indices[i+1:] + indices[i:i+1]
cycles[i] = n - i
else:
j = cycles[i]
indices[i], indices[-j] = indices[-j], indices[i]
print indices
yield tuple(pool[i] for i in indices[:r])
break
else:
return
for x in permutations(xrange(1,6),3):
print x
方式2：
#/usr/bin/env python
# -*-encoding:utf-8 -*-
http://blog.csdn.net/wklken/article/details/8453107
from time import time
#生成全排列
def perm(items, n=None):
lg=len(items)
r=n if n is not None else lg
for i in xrange(lg):
v = items[i:i + 1]
if r == 1:
yield v
else:
rest = items[:i] + items[i + 1:]
for p in perm(rest, r - 1):
yield v + p
#生成组合
def comb(items, n=None):
if n is None:
n = len(items)
for i in xrange(len(items)):
v = items[i:i + 1]
if n == 1:
yield v
else:
rest = items[i + 1:]
for c in comb(rest, n - 1):
yield v + c
if __name__==‘__main__‘:
t=time()
for i in perm(range(1,20),3):
print i
print ‘use time:‘,time()-t
#!/usr/bin/env python
# -*- encoding:utf-8 -*-
from time import time
def permutations(lst,n=None):
num=len(lst)
if num<n:
print ‘n is more than the length of list‘
return
else:
r= num if n is None else n
tmp=range(num)#用tmp值的下标对应mytup的值
cyc=range(num,num-r,-1)#用于循环，保证选出次数
yield [lst[i] for i in tmp[:r]]
while 1:
for i in reversed(range(r)):
cyc[i]-=1
if cyc[i]==0:
tmp[i:]=tmp[i+1:]+tmp[i:i+1]
cyc[i] =num - i
else:
j=cyc[i]
tmp[i],tmp[-j]=tmp[-j],tmp[i]
yield [lst[i] for i in tmp[:r]]
break
else:
return
if __name__==‘__main__‘:
t=time()
for x in permutations(xrange(1,20),3):
print x
print "total run time:",time()-t