Bisect

#coding=utf-8
import random
import bisect


n = random.uniform(0, 6)#在饼图扔骰子
print n
n = random.uniform(0, 6)#在饼图扔骰子
print n
n = random.uniform(0, 6)#在饼图扔骰子    
print n

def weighted_random(items):
    total = sum(w for _,w in items)
    n = random.uniform(0, total)#在饼图扔骰子
    for x, w in items:#遍历找出骰子所在的区间     
        if n<w:
            break
        n -= w
    return x
 
print weighted_random([('iphone', 10), ('ipad', 40), ('itouch', 50)])
print weighted_random([('iphone', 10), ('ipad', 40), ('itouch', 50)])
print weighted_random([('iphone', 10), ('ipad', 40), ('itouch', 50)])
print weighted_random([('iphone', 10), ('ipad', 40), ('itouch', 50)])
print weighted_random([('iphone', 10), ('ipad', 40), ('itouch', 50)])




#coding=utf-8
class WeightRandom:
    def __init__(self, items):
        weights = [w for _,w,_ in items] # weights 是一个数组  数组中的元素来自于items中每个tuple中的w
        self.goods = [x for x,_,_ in items]
        self.total = sum(weights)
        self.acc = list(self.accumulate(weights))
 
    def accumulate(self, weights):#累和.如accumulate([10,40,50])->[10,50,100]
        cur = 0
        for w in weights:
            cur = cur+w
            yield cur
 
    def __call__(self):
        # print 'call acc', self.acc, self.goods
        
        # self.acc 是概率和 [10, 50, 100]
        rand = random.uniform(0, self.total)
        rs = bisect.bisect_right(self.acc , rand)
        print 'rs', rand, rs, self.goods[rs]
        return self.goods[rs] 
 
wr = WeightRandom([('iphone', 10, 10), ('ipad', 40, 10), ('itouch', 50, 10)])

ipadcount = 0
iphonecount = 0
itouchcount = 0

for i in range(1000):
    rs = wr() ##call被调用
    if rs == 'iphone':
        iphonecount += 1
    if rs == 'itouch':
        itouchcount += 1
    if rs == 'ipad':
        ipadcount += 1

print iphonecount, ipadcount, itouchcount


def test():
    items = [('iphone', 10), ('ipad', 40), ('itouch', 50)]
    weights = [w for _,w in items]
    print weights

    def tty(weights):
        cur = 0
        for w in weights:
            cur = cur+w
            yield cur

    rs = tty(weights) #得到一个generator对象
    print 'rs', list(rs) # 一个数组

    
# test()