python字典排序实例详解
本文实例分析了python字典排序的方法。分享给大家供大家参考。具体如下：
1、 准备知识：
在python里，字典dictionary是内置的数据类型，是个无序的存储结构，每一元素是key-value对：
如：dict = {'username'：'password'，'database'：'master'}，其中'username'和'database'是key，而'password'和'master'是value，可以通过d[key]获得对应值value的引用，但是不能通过value得到key。
对于dictionnary，需知道以下几点注意事项：
a、 dictionary 的 key 是大小写敏感的；
b、 一个dictionary中不能有重复的 key；
c、 dictionary是无序的，没有元素顺序的概念，它们只是序偶的简单排列。
2、 字典排序实现：
前面已说明dictionary本身没有顺序概念，但是总是在某些时候，但是我们常常需要对字典进行排序，怎么做呢？下面告诉你：
方法1：最简单的方法，排列元素(key/value对)，然后挑出值。字典的items方法，会返回一个元组的列表，其中每个元组都包含一对项目——键与对应的值。此时排序可以sort()方法。
def sortedDictValues1(adict): items = adict.items() items.sort() return [value for key, value in items]
方法2：使用排列键(key)的方式，挑出值，速度比方法1快。字典对象的keys()方法返回字典中所有键值组成的列表，次序是随机的。需要排序时只要对返回的键值列表使用sort()方法。
def sortedDictValues1(adict): keys = adict.keys() keys.sort() return [adict[key] for key in keys]
方法3：通过映射的方法去更有效的执行最后一步
def sortedDictValues1(adict): keys = adict.keys() keys.sort() return map(adict.get,keys)
方法4：对字典按键排序，用元组列表的形式返回，同时使用lambda函数来进行；
sorted(iterable[, cmp[, key[, reverse]]]
cmp和key一般使用lambda
如：
>>> d={"ok":1,"no":2}#对字典按键排序，用元组列表的形式返回
>>> sorted(d.items, key=lambda d:d[0])
[('no', 2), ('ok', 1)]
对字典按值排序，用元组列表的形式返回
>>> sorted(d.items, key=lambda d:d[1])
[('ok', 1), ('no', 2)]
对字典元素的排序虽然有好多种方法，这里也没有总结全，但如果对程序效率没有太高要求，选择喜欢的用就好。
希望本文所述对大家的Python程序设计有所帮助。
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