Python装饰器

python

1. 函数作用域LEGB

LEGB：L>E>G>B

• L: local 函数内部作用域
• E： enclosing 函数内部与内嵌函数之间
• G: global 全局作用域
• B: build-in 内置作用域

判断一个学生是否及格。

#!/usr/bin/env python
# coding=utf-8
passline = 60
def func(val):
    #passline = 90   
    if val >= passline:
        print ("pass")
    else:
        print ("failed")
    def in_func():
        print (val)
def Max(val1, val2):
    return max(val1,val2)
func(89)

通过上面例子，了解函数作用域和LEGB规则

2. 闭包理解与使用

Closure: 内部函数中对enclosing作用域的变量进行引用。
函数实质与属性
1. 函数是一个对象
2. 函数执行完成后内部变量回收
3. 函数属性
4. 函数返回值

#!/usr/bin/env python
# coding=utf-8
passline = 60
def func(val):
    #passline = 90   
    print ('%x'%id(val))
    if val >= passline:
        print ("pass")
    else:
        print ("failed")
    def in_func():
        print (val)
    in_func()
    return in_func
f = func(89)
f()
print (f.__closure__)

使用闭包

#!/usr/bin/env python
# coding=utf-8
passline = 60
def func_150(val):
    passline = 90
    if val >= passline:
        print ('pass')
    else:
        print ('failed')
def func_100(val):
    passline = 60
    if val >= passline:
        print ('pass')
    else:
        print('failed')
def set_passline(passline):
    def cmp(val):
        if val >= passline:
            print('pass')
        else:
            print ('failed')
    return cmp
f_100 = set_passline(60)
print type(f_100)
print (f_100.__closure__)
f_100(89)
f_100(59)
f_150 = set_passline(90)
f_150(89)

闭包作用
1. 封装
2. 代码复用

#!/usr/bin/env python
# coding=utf-8
def my_sum(*arg):
    # if len(arg) == 0:
    #     return 0
    # for val in arg:
    #     if not isinstance(val, int):
    #         return 0
    return sum(arg)
def my_average(*arg):
    # if len(arg) == 0:
    #     return 0
    # for val in arg:
    #     if not isinstance(val, int):
    #         return 0
    return sum(arg)/len(arg)
# 使用闭包完成
def dec(func):
    def in_dec(*arg):
        if len(arg) == 0:
            return 0
        for val in arg:
            if not isinstance(val, int):
                return 0
        return func(*arg)
    return in_dec
my_sum = dec(my_sum)
my_average = dec(my_average)
print (my_sum(1,2,3,4,5))
print (my_sum(1,2,3,4,5, '6'))
print (my_average(1,2,3,4,5))
print (my_average())                                                                                                                                                    

3. 装饰器

1. 装饰器用来装饰函数
2. 返回一个函数对象
3. 被装饰函数标识符指向返回的函数对象
4. 语法糖 @deco

#!/usr/bin/env python
# coding=utf-8
def dec(func):
    print ("call dec")
    def in_dec(*arg):
        if len(arg) == 0:
            return 0
        for val in arg:
            if not isinstance(val, int):
                return 0
        return func(*arg)
    return in_dec
@dec
def my_sum(*arg):
    # if len(arg) == 0:
    #     return 0
    # for val in arg:
    #     if not isinstance(val, int):
    #         return 0
    return sum(arg)
@dec
def my_average(*arg):
    # if len(arg) == 0:
    #     return 0
    # for val in arg:
    #     if not isinstance(val, int):
    #         return 0
    return sum(arg)/len(arg)
print (my_sum(1,2,3,4,5))
print (my_sum(1,2,3,4,5, '6'))
print (my_average(1,2,3,4,5))
print (my_average())

装饰器等价于闭包调用，使用语法糖可以隐式的调用。

call dec
call dec
15
0
3
0

def deco(func):
    def in_deco(x,y):
        print ('in deco')
        func(x,y)
    print ('call deco')
    return in_deco
# deco(bar) -> in_deco
# bar = in_deco
# bar() in_deco() bar()
@deco
def bar(x,y):
    print ('in bar', x+y)
print (type(bar))
bar(1,2)