Day 12 the closure function / decorator

Closure function

Closure function: the functions and variables wrap

def make_averager():
    series = []

    def averager(new_value):
        series.append(new_value)
        total = sum(series)
        return total/len(series)
    return averager

avg = make_averager()
print(avg(10))
print(avg(20))
print(avg(30))

10.0
15.0
30.0

Decorator

Decorator is a function

Two principles:

1. Without changing the source code of the function to be decorated
2. Do not change the function calls are decorated

def deco(func):
    def wrapper(*args, **kwargs):
        res = func(*args, **kwargs)
        print("I'm Tiny")
        return res

    return wrapper


@deco
def say(x):
    print(f'Hello,{x}')
    return 'Nice to meet you'


say = say('nick')
print(say)

Above the decorator, the last call say () when, in fact, is calling wrapper (), if say () returns a value, then the wrapper () inside also need to return this value, that is, above the res

If you say () need to pass parameters, then the wrapper () should be passed within the same parameters, but because we do not know what to say parameters passed (), all can use * args, ** kwargs universal parameters to represent

python decorator syntax sugar

In the decorative function just above, and is written on a separate line@装饰器名

You can call the function directly be decorated

Three decorator

import time

current_uesr = {'username': None}


def auth(engine='file'):

    def login(func):
        # func = 最原始的index
        def wrapper(*args, **kwargs):

            if current_user['username']:
                res = func(*args, **kwargs)

                return res

            user = input('username: ').strip()
            pwd = input('password: ').strip()

            if engine == 'file':
                print('base of file')
                if user == 'nick' and pwd == '123':
                    print('login successful')
                    current_uesr['usre'] = user
                    res = func(*args, **kwargs)

                    return res
                else:
                    print('user or password error')
            elif engine == 'mysql':
                print('base of mysql, please base of file')
            elif engine == 'mongodb':
                print('base of mongodb, please base of file')
            else:
                print('please base of file')

        return wrapper

    return login


@auth(engine='mysql')
def home(name):
    print(f"welcome {name} to home page")
    time.sleep(1)


@auth(engine='file')
def index():
    print('welcome to index')
    time.sleep(1)


res = index()

username: nick
password: 123
base of file
login successful
welcome to index