1 #!/usr/bin/env python
 2 # -*- coding:utf-8 -*-
 3 import time
 4 def cal(l):
 5     start_time=time.time()
 6     res=0
 7     for i in l:
 8         time.sleep(0.1)
 9         res+=1
10     stop_time=time.time()
11     print('The run time of the function is%s'%(stop_time-start_time))
12     return res
13 print(cal(range(100)))

output

The run time of the function is 10.07073187828064
100

Decorator

The essence is function, and the function is to add additional functions for other functions.

Principle:

Do not modify the source code of the decorated function

Do not modify the call mode of the decorated function

Knowledge reserve of decorators

Decorator = higher order function + function nesting + closure

Higher order function: a function whose receiving parameter or return value is a function.

Function nesting: functions are defined within functions.

 1 #!/usr/bin/env python
 2 # -*- coding:utf-8 -*-
 3 def foo():
 4     time.sleep(3)
 5     print('Come from foo')
 6 import time
 7 #One more time, unqualified
 8 def timer(func):
 9     start_time=time.time()
10     func()
11     stop_time=time.time()
12     print('Function run time is%s'%(stop_time-start_time))
13     return func
14 foo=timer(foo)
15 foo()

output

From foo
Function run time is 3.000976085662842
From foo

It can be seen that only higher-order functions can not realize the decorator.

Frame of decorator

def timmer(func):
def wrapper():
print(func)
func()
return wrapper()

Decorator implementation

 1 #!/usr/bin/env python
 2 # -*- coding:utf-8 -*-
 3 import time
 4 def timmer(func): #func=test
 5     def wrapper(*args,**kwargs):
 6         # print(func)
 7         start_time=time.time()
 8         res=func(*args,**kwargs) #Is running test()
 9         stop_time = time.time()
10         print('Run time is%s' %(stop_time-start_time))
11         return res
12     return wrapper
13 
14 @timmer #test=timmer(test)  Before which function to modify
15 def test(name,age,gender):
16     time.sleep(3)
17     print('test Function completed')
18     return 'This is test Return value'
19 res=test('linhaifeng',18,'male')
20 print(res)

output

test function completed
The operation time is 3.000012159347534
This is the return value of test

How to query two side elements quickly without index

1 #!/usr/bin/env python
2 # -*- coding:utf-8 -*-
3 l=[5,2,4,7,9,2,6,0,3]
4 a,b,*_,c,d=l
5 print(a,b,c,d)

output

5 2 0 3

A fast method of exchange without "bridge"

1 #!/usr/bin/env python
2 # -*- coding:utf-8 -*-
3 f1=1
4 f2=2
5 f1,f2=f2,f1
6 print(f1,f2)

output

2 1

Decorator with parameter verification function

 1 #!/usr/bin/env python
 2 # -*- coding:utf-8 -*-
 3 user_list=[
 4     {'name':'alex','passwd':'123'},
 5     {'name':'linhaifeng','passwd':'123'},
 6     {'name':'wupeiqi','passwd':'123'},
 7     {'name':'yuanhao','passwd':'123'},
 8 ]
 9 current_dic={'username':None,'login':False}
10 
11 def auth(auth_type='filedb'):
12     def auth_func(func):
13         def wrapper(*args,**kwargs):
14             print('The type of certification is',auth_type)
15             if auth_type == 'filedb':
16                 if current_dic['username'] and current_dic['login']:
17                     res = func(*args, **kwargs)
18                     return res
19                 username=input('User name:').strip()
20                 passwd=input('Password:').strip()
21                 for user_dic in user_list:
22                     if username == user_dic['name'] and passwd == user_dic['passwd']:
23                         current_dic['username']=username
24                         current_dic['login']=True
25                         res = func(*args, **kwargs)
26                         return res
27                 else:
28                     print('Wrong user name or password')
29             elif auth_type == 'ldap':
30                 print('How can you play')
31                 res = func(*args, **kwargs)
32                 return res
33             else:
34                 print('The devil knows what authentication method you use')
35                 res = func(*args, **kwargs)
36                 return res
37 
38         return wrapper
39     return auth_func
40 
41 @auth(auth_type='filedb') #auth_func=auth(auth_type='filedb')-->@auth_func Attached a auth_type  --->index=auth_func(index)
42 def index():
43     print('Welcome to Jingdong Homepage')
44 
45 @auth(auth_type='ldap')
46 def home(name):
47     print('Welcome home%s' %name)
48 #
49 @auth(auth_type='sssssss')
50 def shopping_car(name):
51     print('%s In the shopping cart［%s,%s,%s］' %(name,'Tea with milk','Younger sister','A doll'))
52 
53 # print('before-->',current_dic)
54 # index()
55 # print('after--->',current_dic)
56 # home('product manager')
57 shopping_car('product manager')

output

The authentication type is SSSSSS
The devil knows what authentication method you use
In the product manager's shopping cart [milk tea, sister, doll]