如何创建仅继承特定属性的对象的别名

debugcn 发表于 Dev

阿克斯坎

我正在用python编写程序，用户可以在其中添加名称和数字到列表中。我将条目保存在具有2个属性的类中，并将该类的实例另存为列表中的对象：

class NewEntry:
    def __init__(self):
        self.name = ""
        self.number = ""

entry = NewEntry()
entry.name = userinput[1]
entry.number = userinput[2]

entrylist.append(entry)

我现在正在尝试添加一个称为别名的函数，该函数将使用新名称保存一个条目。别名应该以这样一种方式连接到原始条目，即更改别名之一的数量会将每个相应别名的数量更改为相同的值。这是我尝试执行的代码：

for key in entrylist:
    if key.name == userinput[1]:
        entry = key
        entry.name = userinput[2]
        entrylist.append(entry)

这不能按预期工作。创建新别名时，它还会更改key的.name，我试图仅从中继承数字属性。

我也尝试了以下方法：

for key in entrylist:
    if key.name == userinput[1]:
        entry = NewEntry()
        entry.name = userinput[2]
        entry.number = key.number
        entrylist.append(entry)

TL; DR：我希望能够创建一个对象的副本，该对象的.number属性在所有别名中都相同。我希望所有这些对象的名称都不同，但数量保持不变。别名之一的数量更改也会影响其他别名。

Ax319

您可以通过添加一个alias_of属性来链接它们，以表示名称的别名。

如果你有一对起来property为你的number属性，那么你实际控制获取设置哪些对象。

class NewEntry:
    # I added the attributes as constructor
    # arguments since you're setting them anyway
    def __init__(self, name='', number=None, alias_of=None):
        self.name = name
        # since we want self.number to be a property
        # it is common practice to use a _ to signify
        # that an attribute is private
        self._number = number
        # here alias will refer to the instance it's
        # an alias of. It defaults to None
        # or not an alias
        self.alias_of = alias_of
    
    # giving a method a @property decorator
    # makes it get the attribute from here
    # That way you control which number it's getting
    @property
    def number(self):
        if self.alias_of:
            return self.alias_of.number
        else:
            return self._number
    
    # The same is true if you give it a setter
    # method. It controls which instances number
    # that you set
    @number.setter
    def number(self, value):
        if self.alias_of:
            self.alias_of.number = value
        else:
            self._number = value


entry = NewEntry('my name', number=1)
entry2 = NewEntry('my name 2', number=2)
# here we say that entry3 is an alias of entry
entry3 = NewEntry('my other name', alias_of=entry)

print(entry.number)
print(entry2.number)
# and here entry3 is actually setting entry
# 1's number attribute
entry3.number = 3
print(entry.number)

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