老男孩python学习自修第十七天【装饰器】

装饰器：在某个方法执行前后去执行其他新定义的行为

例如：

#!/usr/bin/env python
# _*_ coding:UTF-8 _*_

def before_say_hello():
    print "before hello"

def after_say_hello():
    print "after hello"

def say_hello_wrapper(func):
    def wrapper():
        print "Before"
        before_say_hello()
        func()
        print "After"
        after_say_hello()
    return wrapper

@say_hello_wrapper
def say_hello():
    print "Hello!"

if __name__ == "__main__":
    say_hello()

执行结果：

/Users/liudaoqiang/PycharmProjects/numpy/venv/bin/python /Users/liudaoqiang/Project/python_project/day14/decorator_test.py
Before
before hello
Hello!
After
after hello

Process finished with exit code 0

2.装饰器的执行步骤

（1）首先，装饰器本身也是一个函数，即say_hello_wrapper也是一个函数，也需要在执行前加入到内存

（2）当执行到@say_hello_wrapper时，即将say_hello()替换为say_hello_wrapper()里面的wrapper(), 即为相同的内存地址

（3）当执行到say_hello()时，则会执行say_hello_wrapper()

注意：使用debug模式可知装饰器的执行步骤

3. 带参数函数的装饰器

#!/usr/bin/env python
# _*_ coding:UTF-8 _*_

def before_say_hello():
    print "before hello"

def after_say_hello():
    print "after hello"

def say_hello_wrapper(func):
    def wrapper(content):
        print "Before"
        before_say_hello()
        func(content)
        print "After"
        after_say_hello()
    return wrapper

@say_hello_wrapper
def say_hello(content):
    print "Hello, {0}".format(content)

if __name__ == "__main__":
    say_hello("World")

结果：

/Users/liudaoqiang/PycharmProjects/numpy/venv/bin/python /Users/liudaoqiang/Project/python_project/day14/decorator_test.py
Before
before hello
Hello, World
After
after hello

Process finished with exit code 0

注意：只需将参数加入到wrapper()中即可，因为wrapper()为替换函数

4.带返回值函数的装饰器

#!/usr/bin/env python
# _*_ coding:UTF-8 _*_

def before_say_hello():
    print "before hello"

def after_say_hello():
    print "after hello"

def say_hello_wrapper(func):
    def wrapper(content):
        print "Before"
        before_say_hello()
        ret = func(content)
        print "After"
        after_say_hello()
        return ret
    return wrapper

@say_hello_wrapper
def say_hello(content):
    print "Hello, {0}".format(content)
    return content

if __name__ == "__main__":
    ret = say_hello("World")
    print ret

结果：

/Users/liudaoqiang/PycharmProjects/numpy/venv/bin/python /Users/liudaoqiang/Project/python_project/day14/decorator_test.py
Before
before hello
Hello, World
After
after hello
World

Process finished with exit code 0