Python中的对象类型转换（设计建议）

问题描述

我们假设有一个函数get_pack（），它返回一个Pack对象：

  
 def __init __（self，name，weight）：
 self.name = name 
 self.weight = weight 
 ... 
  
 
 
 
我想要做的是将此对象包装到我的对象中，这就是说，CommercialPack有一些有用的函数：
  class CommercialPack（Pack）：
 def get_delivery_price（self，distance）：
 return self.weight * PER_KM_PRICE * distance 
 ... 
  
然后创建一个返回CommercialPack而不是Pack的函数。在其他语言（如Delphi或Java）中，您可以在运行时键入cast该对象。所以我想有像：
  def get_commercial_pack（）：
 return CommercialPack（get_pack $ b  
然后你有你所需要的一切，没有麻烦。因为我希望我的CommercialPack对象具有Pack对象具有的所有属性和功能。我只是想把它包装在我的新类。基本上我不想这样做：
 类CommercialPack（object）：
 def __init __ ，pack）：
 self.name = pack.name 
 self.weight = pack.weight 
 ... 
  
 OR 
  class CommercialPack（object）：
 def __init __ self，pack）：
 self.pack = pack 
  
 
 
 
非常感谢。
解决方案
可能类似这样
  $ b def __init __（self，pack）：
 self .__ dict __。update（pack .__ dict__）
  
如果你不介意在包和商业包之间共享状态，你甚至可以这样做。
  class CommercialPack对象）：
 def __init __（self，pack）：
 self .__ dict__ = pack .__ dict__ 
  
在你的例子中应该是确定的，因为你不保存对包对象的任何其他引用
 
 
 
例如
 
 
 <$ c $ p>  PER_KM_PRICE = 100 
 
 class Pack（object）：
 def __init __（self，name，weight）：
 self.name = name 
 self.weight = weight 
 
 
 class CommercialPack（Pack）：
 def __init __（self，pack）：
 self .__ dict__ = pack .__ dict__ 
 
 def get_delivery_price（self，distance）：
 return self.weight * PER_KM_PRICE * distance 
 
 def get_pack（）：
 return bmp（pack，20）
 
 cp = CommercialPack（get_pack（））
 print cp.get_delivery_price（3）
  pre> 
Let's say there is a library function called get_pack() which returns a Pack object:
class Pack(object):
    def __init__(self, name, weight):
        self.name = name
        self.weight = weight
        ...
What I want to do is to wrap this object into my object which is let's say CommercialPack which has a couple of useful functions:
class CommercialPack(Pack):
    def get_delivery_price(self, distance):
        return self.weight * PER_KM_PRICE * distance
    ...
And then create a function which returns CommercialPack instead of Pack. In some other languages like Delphi or Java, you can type cast that object on the fly. So I want to have something like:
def get_commercial_pack():
    return CommercialPack(get_pack())
and then you have all you need with no hassle. Because I would like my CommercialPack object to have all the properties and functions that Pack object has. I just want to wrap it inside my new class. Basically I don't want to do something like this:
class CommercialPack(object):
    def __init__(self, pack):
        self.name = pack.name
        self.weight = pack.weight
        ...
OR
class CommercialPack(object):
    def __init__(self, pack):
        self.pack = pack
I'm looking for an elegant solution instead like I said, some kind of type casting or whatever I can do elegantly in Python.
Thanks very much.
 解决方案 
Perhaps something like this
class CommercialPack(object):
    def __init__(self, pack):
        self.__dict__.update(pack.__dict__)
You can even do this if you don't mind sharing state between the pack and the commercial pack
class CommercialPack(object):
    def __init__(self, pack):
        self.__dict__ = pack.__dict__
It should be ok in your example since you aren't keeping any other references to the pack object
eg.
PER_KM_PRICE = 100

class Pack(object):
    def __init__(self, name, weight):
        self.name = name
        self.weight = weight


class CommercialPack(Pack):
    def __init__(self, pack):
        self.__dict__ = pack.__dict__

    def get_delivery_price(self, distance):
        return self.weight * PER_KM_PRICE * distance

def get_pack():
    return Pack("pack", 20)

cp = CommercialPack(get_pack())
print cp.get_delivery_price(3)
                        
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