Use of sort method and sorted function in python3

Python list has a built-in sort() method for sorting. You can also use Python’s built-in global sorted() method to sort an iterable sequence to generate a new sequence.

1 Basic form

The list has its own sort method, which sorts the list in-situ. Tuples are not allowed, tuples cannot be modified

>>> a = [3,6,1,8,0,5,7,9,2,4]
>>> a.sort()
>>> a
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

>>> a = [3,6,1,8,0,5,7,9,2,4]
>>> res = sorted(a)
>>> a
[3, 6, 1, 8, 0, 5, 7, 9, 2, 4]
>>> res
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

2 Complex list

2.1 The content of the list is a tuple

student = [
    ('john', 'A', 15),
    ('jane', 'B', 12),
    ('dave', 'B', 10),
]
res = sorted(student, key=lambda student: student[2])   # sort by age
print(res)

operation result:

2.2 List content is class

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))

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

res = sorted(students, key=lambda s: s.age)
print(res)

2.3 The content of the list is a dictionary

student = [
    {
    
    "name": "xiaoming", "score": 60},
    {
    
    "name": "daxiong", "score": 20},
    {
    
    "name": "maodou", "score": 30},
]

res = sorted(student, key=lambda d:d['score'])
print(res)

2.4 itemgetter and attrgetter

Python provides operator.itemgetter and attrgetter to improve execution speed

from operator import itemgetter, attrgetter

stu = [
    ("A", 30),
    ("B", 20),
    ("C", 10)
]

print(sorted(stu, key=itemgetter(1)))
#operator提供了多个字段的复杂排序，先对第0个字段排序，再对第一个字段排序
print(sorted(stu, key=itemgetter(0,1)))

from operator import itemgetter, attrgetter
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))


stu = [
    Student('jane', 'B', 12),
    Student('john', 'A', 12),
    Student('dave', 'B', 10),
]
# 对students按照年龄排序
print(sorted(stu, key=attrgetter('age')))
# 其等价于
print(sorted(stu, key=lambda o: o.age))

# 也可以按多个key排序, 先按age再按grade排序
print(sorted(stu, key=attrgetter('age', 'grade')))

operation result:

3 Sort the dictionary

Sorting the dictionary returns a list, you can sort the key, you can sort the value, you can also sort the items

d = {
    
    1: 'D', 2: 'C', 3: 'B', 4: 'A'}
print(sorted(d))
print(sorted(d.values()))
print(sorted(d.items()))

operation result

4 cmp_to_key (customized comparison function)

After python3, the cmp parameter in the sort method and the sorted function is cancelled. If you still need to use a custom comparison function, you can use the cmp_to_key function. Use with tools that accept key function (such as sorted(), min(), max(), heapq.nlargest(), itertools.groupby())

from functools import cmp_to_key

a = [3, 6, 1, 8, 0, 5, 7, 9, 2, 4]


def cmp(x, y):
    if x > y:
        return -1
    elif x < y:
        return 1
    else:
        return 0

b = sorted(a, key=cmp_to_key(cmp))
print(b)

operation result