【python练习】--《learn python the hard way》ex39

————————

正在学《learn python the hard way》（笨方法学Python），

发一篇在ex39练习hashmap时，自己敲的一些注释，希望对学着学着就卡在这的朋友们有点作用，

最后附上文件。

# -*- coding: utf-8 -*-#Copyright XD#hashmap是以两级列表实现字典功能的轮子，能帮助理解字典。#aMap是数据,key是小列表(里层列表)的第一个元素，value是小列表的第二个元素#使用哈希函数，获得每一个小列表的id(哈希值模除列表长度)，方便查找#i 是通过enumberate函数，获得的index（位置、索引），#i 用来确定小列表是不是空的，方便下面的list()遍历非空小列表def new(num_bucket=256):"""Initializes a Map with the given number of buckets."""#创建256个篮子aMap = []for i in range(0,num_bucket):aMap.append([])return aMapdef hash_key(aMap,key):"""Given a key this will create a number and then convert it to\an index for the aMap's buckets."""return hash(key) % len(aMap)#获得一个放置key值的位置#%代表求模运算，取余数，这里用%是为了最小化最大数，不然单纯的hash(key)得出的是一个很大的数字def get_bucket(aMap,key):"""Given a key, find the bucket where it would go."""bucket_id = hash_key(aMap,key)return aMap[bucket_id] def get_slot(aMap,key,default=None):"""Return the index,key,and the value of a slot found in a bucket.Return -1,key,and default(None if not set)when not found."""bucket = get_bucket(aMap,key)for i , kv in enumerate(bucket):  #enumerate函数用于遍历列表内容及其索引(位置)，先显示下标，再显示内容。k,v = kvif key == k:return i,k,vreturn -1,key,defaultdef get(aMap, key,default=None):"""Gets the value in a bucket for the given key, or the default."""i,k,v = get_slot(aMap,key,default=default)return vdef set(aMap,key,value):"""Sets the key to the value, replacing any existing value."""bucket = get_bucket(aMap,key)i,k,v = get_slot(aMap,key)if i >=0:# the key exits,replace itbucket[i] = (key, value)else:#the key does not , append to create itbucket.append((key, value))def delete(aMap, key):"""Deletes the given ket from the map."""bucket = get_bucket(aMap, key)#使用xrange做循环要比用range的性能更好，尤其是在返回值很大的时候。#使用range会直接生成一个列表，而xrange不会，xrange返回一个生成器。for i in xrange(len(bucket)):k, v = bucket[i]if key == k:del bucket[i]breakdef list(aMap):"""Print out what's in the map."""for bucket in aMap:if bucket: #当bucket不为空时，打印出来（遍历）for k, v in bucket:print k, v

下面是测试，书里也有，还是贴上来吧

import hashmap#create a mapping of state to abbreviationstates = hashmap.new()hashmap.set(states,"Oregon","OR")hashmap.set(states, 'Florida', 'FL')hashmap.set(states, 'California', 'CA')hashmap.set(states, 'New York', 'NY')hashmap.set(states, 'Michigan', 'MI')# create a basic set of states and some cities in themcities = hashmap.new()hashmap.set(cities, 'CA', 'San Francisco')hashmap.set(cities, 'MI', 'Detroit')hashmap.set(cities, 'FL', 'Jacksonville')# add some more citieshashmap.set(cities, 'NY', 'New York')hashmap.set(cities, 'OR', 'Portland')# print out some citiesprint '-' * 10print "NY State has: %s" % hashmap.get(cities, 'NY')print "OR State has: %s" % hashmap.get(cities, 'OR')# print some statesprint '-' * 10print "Michigan's abbreviation is: %s" % hashmap.get(states, 'Michigan')print "Florida's abbreviation is: %s" % hashmap.get(states, 'Florida')# do it by using the state then cities dictprint '-' * 10print "Michigan has: %s" % hashmap.get(cities, hashmap.get(states, 'Michigan'))print "Florida has: %s" % hashmap.get(cities, hashmap.get(states, 'Florida'))# print every state abbreviationprint '-' * 10hashmap.list(states)# print every city in stateprint '-' * 10hashmap.list(cities)print '-' * 10state = hashmap.get(states, 'Texas')if not state:  print "Sorry, no Texas."# default values using ||= with the nil result# can you do this on one line?city = hashmap.get(cities, 'TX', 'Does Not Exist')print "The city for the state 'TX' is: %s" % city

新年第一发，

新年快乐~