將方法作為變數分配給物件

我希望物件在它們的例程中呼叫某個方法（在變數中分配的特定方法）。我設法用 dict 來做到這一點，我還設法通過在創建物件后分配變數來做到這一點。哪種方式更好？還有其他更清潔的方法嗎？

第一種作業方式（字典）：

class Foo:
    def __init__(self, name, funcin) -> None:
        self.name = name
        self.func = {
            'bear': self.bear,
            'boar': self.boar,
        }[funcin]
    
    def routine(self):
        print('fluff')
        self.func()

    def bear(self):
        print(f'I, {self.name}, am a bear and I like honey.')
    
    def boar(self):
        print(f'I, {self.name}, am a boar and I like fruits.')

bob = Foo('bob', 'bear')
mark = Foo('mark', 'boar')

bob.routine()
mark.routine()

第二種作業方式（另一行分配）：

class Foo:
    def __init__(self, name) -> None:
        self.name = name
    
    def routine(self):
        print('fluff')
        self.func()

    def bear(self):
        print(f'I, {self.name}, am a bear and I like honey.')
    
    def boar(self):
        print(f'I, {self.name}, am a boar and I like fruits.')
    
Kona = Foo('Kona')
Kona.func = Kona.bear
John = Foo('John')
John.func = John.boar

Kona.routine()
John.routine()

無效的方法：

# NameError: name 'bear' is not defined
class Foo:
    def __init__(self, name, funcin) -> None:
        self.name = name
        self.func = self.funcin
    def bear(self):
        print(f'I, {self.name}, am a bear and I like honey.')
bob = Foo('bob', bear)
bob.func()

# NameError: name 'self' is not defined
class Foo:
    def __init__(self, name, funcin) -> None:
        self.name = name
        self.func = funcin
    def bear(self):
        print(f'I, {self.name}, am a bear and I like honey.')
bob = Foo('bob', self.bear)
bob.func()

# NameError: name 'Kim' is not defined
class Foo:
    def __init__(self, name, funcin) -> None:
        self.name = name
        self.func = funcin
    def bear(self):
        print(f'I, {self.name}, am a bear and I like honey.')
Kim = Foo('Kim', Kim.bear)
Kim.func()   

# TypeError: Foo.bear() missing 1 required positional argument: 'self'
class Foo:
    def __init__(self, name, funcin) -> None:
        self.name = name
        self.func = funcin
    def bear(self):
        print(f'I, {self.name}, am a bear and I like honey.')
bob = Foo('bob', Foo.bear)
bob.func()

uj5u.com熱心網友回復：

類的方法就像它們通過類的__dict__屬性在字典中一樣可用。所以在你提出的第一個解決方案中，你也可以self.func這樣定義：

self.func = Foo.__dict__[funcin].__get__(self)

因此，通過__dict__[funcin]我們從類物件中檢索方法，__get__我們得到一個具有正確self系結的函式。

為了使它更通用，以便您不必提及Foo：

self.func = self.__class__.__dict__[funcin].__get__(self)

uj5u.com熱心網友回復：

一個常見的解決方案是類繼承。從抽象基類到 mixin 有多種選擇，但這里是一個簡單的開始

class Foo:
    def __init__(self, name) -> None:
        self.name = name
        
    def func(self):
        raise NotImplementedError
    
    def routine(self):
        print('fluff')
        self.func()

class Bear(Foo):
    
    def func(self):
        print(f'I, {self.name}, am a bear and I like honey.')
    
class Boar(Foo):
    
    def func(self):
        print(f'I, {self.name}, am a boar and I like fruits.')

bob = Bear('bob')
mark = Boar('mark')

bob.routine()
mark.routine()

uj5u.com熱心網友回復：

您可以使用 getattr()：

class Foo:
    def __init__(self, name, funcin) -> None:
        self.name = name
        self.func = getattr(self,funcin)
    
    def routine(self):
        print('fluff')
        self.func()

    def bear(self):
        print(f'I, {self.name}, am a bear and I like honey.')
    
    def boar(self):
        print(f'I, {self.name}, am a boar and I like fruits.')

如果您不需要執行額外的（常見）絨毛，您可以簡單地分配self.routine = getattr(self,funcin)甚至不定義routine() 函式。

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