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