#!/usr/local/bin/python2.7
#coding=gbk
'''
Created on 2012年11月7日

@author: palydawn
'''
import cmath
from BitVector import BitVector

class BloomFilter(object):
 #之前用python写了一个网络爬虫,里面url去重用的就是布隆过滤器,不过那个是用c++写的,在windows下用boost编译成python模块之后再python里面调用,现在用纯python重新写一个,这样爬虫在linux和windows下都可以运行了,下面是代码:
 def __init__(self, error_rate, elementNum):
 #计算所需要的bit数
 self.bit_num = -1 * elementNum * cmath.log(error_rate) / (cmath.log(2.0) * cmath.log(2.0))
 
 #四字节对齐
 self.bit_num = self.align_4byte(self.bit_num.real)
 
 #分配内存
 self.bit_array = BitVector(size=self.bit_num)
 
 #计算hash函数个数
 self.hash_num = cmath.log(2) * self.bit_num / elementNum
 
 self.hash_num = self.hash_num.real
 
 #向上取整
 self.hash_num = int(self.hash_num) + 1
 
 #产生hash函数种子
 self.hash_seeds = self.generate_hashseeds(self.hash_num)
 
 def insert_element(self, element):
 for seed in self.hash_seeds:
 hash_val = self.hash_element(element, seed)
 #取绝对值
 hash_val = abs(hash_val)
 #取模,防越界
 hash_val = hash_val % self.bit_num
 #设置相应的比特位
 self.bit_array[hash_val] = 1
 
 #检查元素是否存在,存在返回true,否则返回false 
 def is_element_exist(self, element):
 for seed in self.hash_seeds:
 hash_val = self.hash_element(element, seed)
 #取绝对值
 hash_val = abs(hash_val)
 #取模,防越界
 hash_val = hash_val % self.bit_num
 
 #查看值
 if self.bit_array[hash_val] == 0:
 return False
 return True
 
 #内存对齐 
 def align_4byte(self, bit_num):
 num = int(bit_num / 32)
 num = 32 * (num + 1)
 return num
 
 #产生hash函数种子,hash_num个素数
 def generate_hashseeds(self, hash_num):
 count = 0
 #连续两个种子的最小差值
 gap = 50
 #初始化hash种子为0
 hash_seeds = []
 for index in xrange(hash_num):
 hash_seeds.append(0)
 for index in xrange(10, 10000):
 max_num = int(cmath.sqrt(1.0 * index).real)
 flag = 1
 for num in xrange(2, max_num):
 if index % num == 0:
 flag = 0
 break
 
 if flag == 1:
 #连续两个hash种子的差值要大才行
 if count > 0 and (index - hash_seeds[count - 1]) < gap:
 continue
 hash_seeds[count] = index
 count = count + 1
 
 if count == hash_num:
 break
 return hash_seeds
 
 def hash_element(self, element, seed):
 hash_val = 1
 for ch in str(element):
 chval = ord(ch)
 hash_val = hash_val * seed + chval
 return hash_val
'''
#测试代码
bf = BloomFilter(0.001, 1000000)
element = 'palydawn'
bf.insert_element(element)
print bf.is_element_exist('palydawn')'''

 其中使用了BitVector库,python本身的二进制操作看起来很麻烦,这个就简单多了