英文:
python decorating an object with @
问题
以下是您的代码的翻译部分：
class Sandwich():
height = 5
width = 8
def ingredients(self):
print("我有面包")
class Cheese_decorator():
def __init__(self, obj):
self.obj = obj
# 在这里还有其他内容，使得传递的对象除了下面要装饰的方法之外，变得与原对象相同
# 被装饰的方法
def ingredients(self):
self.obj.ingredients()
print("我还有奶酪")
# 在这里可以添加其他要装饰的方法
sandwich = Sandwich() # 这个三明治不会被装饰
cheese_sandwich = Cheese_decorator(Sandwich()) # 这个三明治被装饰了
sandwich.ingredients() # 输出我有面包
cheese_sandwich.ingredients() # 输出我有面包我还有奶酪
至于您提到的使用@语法的方式来创建装饰对象的问题，Python的@语法通常用于装饰器，而不是用于创建装饰对象。如果您想要将装饰对象赋给变量，可以按照您之前的方式创建Cheese_decorator的实例。
英文:
I want to achieve the decorator design pattern in python using the @ syntax, my code:
class Sandwich():
height = 5
width = 8
def ingredients(self):
print("I have bread")
class Cheese_decorator():
def __init__(self,obj):
self.obj = obj
#something else here so the object becomes the same as the passed one except for the methods to decorate below
#decorated method
def ingredients(self):
self.obj.ingredients()
print("I also have cheese")
#any other method to decorate here
sandwich = Sandwich() # this sandwich wont be decorated
cheese_sandwich = Cheese_decorator(Sandwich()) # this sandwich is decorated
sandwich.ingredients() # prints I have bread
cheese_sandwich.ingredients() # prints I have bread I also have cheese
is there anything I can do like:
sandwich = Sandwich()
cheese_sandwich = @Cheese_decorator
sandwich
?
I want to have the decorated object as a var
答案1
得分: 2
无论你读到什么理论性的文本关于“装饰器模式”——这不是 Python 中装饰器的本质。
@ 语法用于转换函数或类，通常结果本身可调用。如果对类进行装饰，结果将是修改过的类（或新类），它将创建实例，而不是像你的例子中那样直接创建实例。
此外，由于它可应用于 def 或 class 块，装饰对象的结果名称是语句中给出的名称（def 后面或 class 关键字后面的名称）。它还意味着 @ 语法与一个语句组合，并且因此不是一个“表达式”，因此无效于赋值右侧或其他任意位置：@decorator 语法要求它自成一行。
也就是说，你的代码示例，使用 cheese_sandwich = Cheese_decorator(Sandwich()) 正如它所示，符合书上所述的“装饰器模式”，你可以这样称呼它。只是它在 Python 中不符合“装饰器语法”。
英文:
Regardless of whatever theoretical text you got to read "decorator pattern" - that is not what decorators are in Python.
The @ syntax is meant to transform either a function or a class - and usually, the result is callable itself. If a class is decorated, the result is the class modified (or a new class), that will create instances, not instances themselves, like in your example.
Moreover, as it is applicable either on a def or on a class block, the resulting name for the decorated object is the name given in the statement. (Either the name after def or after the class keyword). It also implies the @ syntax composes with one statement, and therefore is not an "expression" - and therefore invalid on the right side of an assignment, or other arbitrary places: the @decorator syntax requires it to be in a line by itself.
That said, your code example, using the the cheese_sandwich = Cheese_decorator(Sandwich()) as it is, conforms with the "decorator pattern" from text books, and you may call it so. It just won't work with the "decorator syntax" from Python.
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