散列函数将输入映射到数字。

1.必须是一致的，apple每次都返回4。

2.不同的内容，映射不同的数字，输入什么都返回4就没有意义了。

散列，hash。

book = dict()book['apple'] = 0.67book['milk']  = 1.49book['avocado'] = 1.49print(book) #{'apple': 0.67, 'milk': 1.49, 'avocado': 1.49}print(book['apple']) #0.67

检测是否已经投票

voted = {}def check_voter(name):    if voted.get(name):        print ("kick them out!")    else:        voted[name] = True        print ("let them vote!")check_voter("tom")  # let them vote!check_voter("mike") # let them vote!check_voter("mike") # kick them out!

应用于缓存处理

cache = {}def get_page(url):    if cache.get(url):        print("缓存获取");        return cache[url]    else:        print("第一次获取");        data = get_data_from_server(url)        cache[url] = data        return datadef get_data_from_server(url):    return url+"数据";print(get_page("cnblogs.com")); #第一次获取 cnblogs.com数据print(get_page("cnblogs.com")); #缓存获取 cnblogs.com数据