装饰器

函数对修改封闭，对扩展开放
例子：
1.对函数的执行时间进行检测
import time
def foo():
    start = time.time()
    print('foo....')
    time.sleep(2)
    end = time.time()
    print('spend %s' % (end - start))
def test():
    start = time.time()
    print('test....')
    time.sleep(2)
    end = time.time()
    print('spend %s' % (end - start))
foo()
test()
问题：一旦修改，所有函数都会改变，并且对更多的函数进行同样操作的话，就会使代码出现大量的重复

2.改进方法,定义show_time函数
def foo():
    print('foo....')
    time.sleep(2)

def show_time(f):
    start = time.time()
    f()
    end = time.time()
    print('spend %s' % (end - start))
show_time(foo)
问题：该方法改变了原生函数的调用方式

3.引入装饰器，装饰器就是为之前的函数添加新的功能
def foo():
    print('foo....')
    time.sleep(2)

def test():
    print('test....')
    time.sleep(2)

def show_time(f):
    def inner():
        start = time.time()
        f()
        end = time.time()
        print('spend %s' % (end - start))
    return inner

foo = show_time(foo)
foo()
test = show_time(test)
test()

4.python的优雅写法
def show_time(f):
    def inner():
        start = time.time()
        f()
        end = time.time()
        print('spend %s' % (end - start))
    return inner

@show_time # test = show_time(test)
def test():
    print('test....')
    time.sleep(2)
test() #test执行部分从test到了show_time

5.再次优化
def show_time(f):
    def inner(*x, **y):
        start = time.time()
        f(*x, **y)
        end = time.time()
        print('spend %s' % (end - start))
    return inner

@show_time
def add(*a, **b):
    print(sum(a),sum(b[i] for i in b))
    time.sleep(1)
add(1, 2, 5, 6, x=5, y=8)

6.装饰器加参数，直接加入无法传参
def logger(flag=''):
    def show_time(f):
        def inner(*x, **y):
            start = time.time()
            f(*x, **y)
            end = time.time()
            print('spend %s' % (end - start))
            if flag=='true':
                print('日志记录')
        return inner
    return show_time

@logger('true') # @show_time
def add(*a, **b):
    print(sum(a),sum(b[i] for i in b))
    time.sleep(1)
add(1, 2, 5, 6, x=5, y=8)

装饰器注意无参数情况下必须两层，即show_time下必须存在inner，有参数情况下要有三层

实战运用：编写一个网页登陆

# 实现
# 1.提示用户选择页面
# 2.检测是否登陆，没有登陆时需要登陆，登陆则进入页面
# 3.登陆模式可以选择

# 自定义一个用户 'lql', '123456'
user, passwd = 'lql', '123456'
login_status = False

# 登陆装饰器，判断是否登陆，判断登陆方式
def login_type(auth_type='jindong'):
    def login(f):
        def test():
            global login_status
            if not login_status:
                if auth_type == 'jindong':
                    username = input('username:')
                    password = input('password:')
                    if user == username and passwd == password:
                        print('welcome...')
                        f()
                        login_status = True
                elif auth_type == 'weixin':
                    username = input('weixinusername:')
                    password = input('weixinpassword:')
                    if user == username and passwd == password:
                        print('welcome...')
                        f()
                        login_status = True
            else:
                f()
        return test
    return login

# 页面的调用
@login_type(auth_type='jindong')
def home():
    print('welcome to home page')

@login_type(auth_type='weixin')
def finance():
    print('welcome to finance page')

@login_type()
def book():
    print('welcome to book page')

# 生成一个存储页面的列表
page = ['home', 'finance', 'login']
for i in range(3):
    print(i+1,page[i])

page_name = None

# 实现选择页面
while page_name != 'q':
    page_name = input('>>')
    if page_name == '1':
        home()
    elif page_name == '2':
        finance()
    elif page_name == '3':
        book()