python sorted

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https://docs.python.org/2/howto/sorting.html

1. 基本排序

mylist = [5, 2, 3, 1, 4]print(sorted(mylist))

[1, 2, 3, 4, 5]

返回新的有序的list，当然你也可以使用list的sort方法，list的sort方法改变原始的list，并且返回None

mylist = [5, 2, 3, 1, 4]mylist.sort()print(mylist)

[1, 2, 3, 4, 5]

list的sort方法只能应用在list上，但是sorted方法接受任何可迭代的对象，比如：

mylist = sorted({1: 'D', 2: 'B', 3: 'B', 4: 'E', 5: 'A'})print(mylist)

[1, 2, 3, 4, 5]

2. key参数

sorted定义了key参数，这个参数需要传递一个method对象

mylist = sorted("This is a test string from Andrew".split(),key=str.lower)print(mylist)

['a', 'Andrew', 'from', 'is', 'string', 'test', 'This']

使用对象索引排序：

student_tuples = [('john', 'A', 15),('jane', 'B', 12),('dave', 'B', 10),]mylist = sorted(student_tuples, key=lambda student: student[2])print(mylist)

[('dave', 'B', 10), ('jane', 'B', 12), ('john', 'A', 15)]

使用对象属性排序：

class Student:    def __init__(self, name, grade, age):        self.name = name        self.grade = grade        self.age = age    def __repr__(self):        return repr((self.name, self.grade, self.age))student_objects = [Student('john', 'A', 15),Student('jane', 'B', 12),Student('dave', 'B', 10),]mylist = sorted(student_objects, key=lambda student: student.age)print(mylist)

[('dave', 'B', 10), ('jane', 'B', 12), ('john', 'A', 15)]

3 Operator模块

from operator import itemgetter, attrgetterclass Student:    def __init__(self, name, grade, age):        self.name = name        self.grade = grade        self.age = age    def __repr__(self):        return repr((self.name, self.grade, self.age))student_objects = [Student('john', 'A', 15),Student('jane', 'B', 12),Student('dave', 'B', 10),]student_tuples = [    ('john', 'A', 15),    ('jane', 'B', 12),    ('dave', 'B', 10),]mylist = sorted(student_objects, key = attrgetter('age'))print(mylist)mylist2 = sorted(student_tuples, key = itemgetter(2))print(mylist2)

[('dave', 'B', 10), ('jane', 'B', 12), ('john', 'A', 15)]
[('dave', 'B', 10), ('jane', 'B', 12), ('john', 'A', 15)]

多个维度排序：

from operator import itemgetter, attrgetterclass Student:    def __init__(self, name, grade, age):        self.name = name        self.grade = grade        self.age = age    def __repr__(self):        return repr((self.name, self.grade, self.age))student_objects = [Student('john', 'A', 15),Student('jane', 'B', 12),Student('dave', 'B', 10),]student_tuples = [    ('john', 'A', 15),    ('jane', 'B', 12),    ('dave', 'B', 10),]mylist = sorted(student_objects, key = attrgetter('grade','age'))print(mylist)mylist2 = sorted(student_tuples, key = itemgetter(1,2))print(mylist2)

[('john', 'A', 15), ('dave', 'B', 10), ('jane', 'B', 12)]
[('john', 'A', 15), ('dave', 'B', 10), ('jane', 'B', 12)]

使用operator.methodcaller()调用对象的方法：调用字符串的count方法

from operator import methodcallermessages = ['critical!!!', 'hurry!', 'standby', 'immediate!!']mylist = sorted(messages, key=methodcaller('count', '!'))print(mylist)

['standby', 'hurry!', 'immediate!!', 'critical!!!']

4. 升序降序

使用reserve参数，降序排序

from operator import itemgetter, attrgetterclass Student:    def __init__(self, name, grade, age):        self.name = name        self.grade = grade        self.age = age    def __repr__(self):        return repr((self.name, self.grade, self.age))student_objects = [Student('john', 'A', 15),Student('jane', 'B', 12),Student('dave', 'B', 10),]student_tuples = [    ('john', 'A', 15),    ('jane', 'B', 12),    ('dave', 'B', 10),]mylist = sorted(student_objects, key = attrgetter('age'),reverse= True)print(mylist)mylist2 = sorted(student_tuples, key = itemgetter(2),reverse = True)print(mylist2)

[('john', 'A', 15), ('jane', 'B', 12), ('dave', 'B', 10)]
[('john', 'A', 15), ('jane', 'B', 12), ('dave', 'B', 10)]

稳定的排序算法，也就是说如果相同的对象，还是原来的顺序，原来谁在前排序后还是谁在前

data = [('red', 1), ('blue', 1), ('red', 2), ('blue', 2)]mylist = sorted(data, key=itemgetter(0))print(mylist)

[('blue', 1), ('blue', 2), ('red', 1), ('red', 2)]

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