【python】装饰器！property和setter用法（python@property装饰器的原理）

【python】装饰器！property和setter用法（python@property装饰器的原理）

文章目录

​​1.引子：函数也是对象​​​​2.函数内的函数​​​​3.装饰器小栗子​​​​5.property和setter用法​​​​reference​​

1.引子：函数也是对象

木有括号的函数那就不是在调用。

def hi(name="yasoob"): return "hi " + name print(hi())# output: 'hi yasoob' # 我们甚至可以将一个函数赋值给一个变量，比如greet = hi# 我们这里没有在使用小括号，因为我们并不是在调用hi函数# 而是在将它放在greet变量里头。我们尝试运行下这个 print(greet())# output: 'hi yasoob' # 如果我们删掉旧的hi函数，看看会发生什么！del hiprint(hi())#outputs: NameError print(greet())#outputs: 'hi yasoob'

2.函数内的函数

（1）在python中，一个函数内能嵌套定义另一个函数，并且可以在该大函数内调用该小函数。

def hi(name="yasoob"): print("now you are inside the hi() function") def greet(): return "now you are in the greet() function" def welcome(): return "now you are in the welcome() function" print(greet()) print(welcome()) print("now you are back in the hi() function") hi()#output:now you are inside the hi() function# now you are in the greet() function# now you are in the welcome() function# now you are back in the hi() function # 上面展示了无论何时你调用hi(), greet()和welcome()将会同时被调用。# 然后greet()和welcome()函数在hi()函数之外是不能访问的，比如： greet()#outputs: NameError: name 'greet' is not defined

（2）开始神奇的是，大函数的返回值可以是一个函数：

def hi(name="yasoob"): def greet(): return "now you are in the greet() function" def welcome(): return "now you are in the welcome() function" if name == "yasoob": return greet #这里！！ else: return welcome a = hi()print(a)#outputs: #上面清晰地展示了`a`现在指向到hi()函数中的greet()函数#现在试试这个 print(a())#outputs: now you are in the greet() function

在 if/else 语句中我们返回 greet 和 welcome，而不是 greet() 和 welcome()。 为什么那样？这是因为当你把一对小括号放在后面，这个函数就会执行；然而如果你不放括号在它后面，那它可以被到处传递，并且可以赋值给别的变量而不去执行它。

当我们写下 a = hi()，hi() 会被执行，而由于 name 参数默认是 yasoob，所以函数 greet 被返回了。

PS：如果我们打印出 hi()()，这会输出 now you are in the greet() function。

（3）最后要说的是函数作为参数传入一个函数：

def hi(): return "hi yasoob!" def doSomethingBeforeHi(func): print("I am doing some boring work before executing hi()") print(func()) doSomethingBeforeHi(hi)#outputs:I am doing some boring work before executing hi()# hi yasoob!

3.装饰器小栗子

终于来到了带@的装饰器，其实就是带了@帽子的函数作为参数，传入@后面的函数中。

def a_new_decorator(a_func): def wrapTheFunction(): print("I am doing some boring work before executing a_func()") a_func() print("I am doing some boring work after executing a_func()") return wrapTheFunction@a_new_decoratordef a_function_requiring_decoration(): """Hey you! Decorate me!""" print("I am the function which needs some decoration to " "remove my foul smell") a_function_requiring_decoration()#outputs: I am doing some boring work before executing a_func()# I am the function which needs some decoration to remove my foul smell# I am doing some boring work after executing a_func() #the @a_new_decorator is just a short way of saying:a_function_requiring_decoration = a_new_decorator(a_function_requiring_decoration)

上面的代码等价于我们熟悉的：

def a_new_decorator(a_func): def wrapTheFunction(): print("I am doing some boring work before executing a_func()") a_func() print("I am doing some boring work after executing a_func()") return wrapTheFunction def a_function_requiring_decoration(): print("I am the function which needs some decoration to remove my foul smell") a_function_requiring_decoration()#outputs: "I am the function which needs some decoration to remove my foul smell" a_function_requiring_decoration = a_new_decorator(a_function_requiring_decoration)#now a_function_requiring_decoration is wrapped by wrapTheFunction() a_function_requiring_decoration()#outputs:I am doing some boring work before executing a_func()# I am the function which needs some decoration to remove my foul smell# I am doing some boring work after executing a_func()

不过一开始上面被装饰过的函数名字已经悄悄发生“改变”，如果print下可以看出（如下代码）。解决方案： @wraps接受一个函数来进行装饰，并加入了复制函数名称、注释文档、参数列表等等的功能。这可以让我们在装饰器里面访问在装饰之前的函数的属性。

print(a_function_requiring_decoration.__name__)# Output: wrapTheFunction

最终加上@wraps的代码如下：

from functools import wraps def a_new_decorator(a_func): @wraps(a_func) def wrapTheFunction(): print("I am doing some boring work before executing a_func()") a_func() print("I am doing some boring work after executing a_func()") return wrapTheFunction @a_new_decoratordef a_function_requiring_decoration(): """Hey yo! Decorate me!""" print("I am the function which needs some decoration to " "remove my foul smell") print(a_function_requiring_decoration.__name__)# Output: a_function_requiring_decoration

5.property和setter用法

reference

​​https://runoob.com/w3cnote/python-func-decorators.html​​

版权声明：本文内容由网络用户投稿，版权归原作者所有，本站不拥有其著作权，亦不承担相应法律责任。如果您发现本站中有涉嫌抄袭或描述失实的内容，请联系我们jiasou666@gmail.com 处理，核实后本网站将在24小时内删除侵权内容。