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super()函數(shù)調(diào)用父類構(gòu)造函數(shù)。在Python中，調(diào)用父類的構(gòu)造函數(shù)通常有兩種方法：super()函數(shù)和self.__class__.initialize()方法，這兩種方法都可以實(shí)現(xiàn)調(diào)用父類的構(gòu)造函數(shù)，但它們的使用場(chǎng)景和方式有所不同，本文將詳細(xì)介紹這兩種方法的原理、使用方法以及相關(guān)問(wèn)題與解答。
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super()函數(shù)
1、原理
super()函數(shù)是Python中的一個(gè)內(nèi)置函數(shù)，用于調(diào)用父類的方法，它可以避免硬編碼父類的名稱，提高代碼的可維護(hù)性，當(dāng)子類需要重寫或擴(kuò)展父類的方法時(shí)，可以使用super()函數(shù)來(lái)調(diào)用父類的原始實(shí)現(xiàn)。
2、使用方法
使用super()函數(shù)調(diào)用父類構(gòu)造函數(shù)的方法如下：
class Parent:
def __init__(self):
print("Parent constructor")
class Child(Parent):
def __init__(self):
super().__init__()
print("Child constructor")
c = Child()
輸出結(jié)果：
Parent constructor Child constructor
3、注意事項(xiàng)
super()函數(shù)只能用于調(diào)用父類的方法，不能用于調(diào)用父類的屬性，如果需要訪問(wèn)父類的屬性，可以直接使用self.__class__.attribute的方式。
如果子類沒(méi)有定義父類的所有方法，super()函數(shù)會(huì)自動(dòng)調(diào)用父類的默認(rèn)實(shí)現(xiàn)，如果需要覆蓋父類的默認(rèn)實(shí)現(xiàn)，可以在子類中重新定義該方法。
如果子類定義了多個(gè)同名方法，super()函數(shù)會(huì)根據(jù)方法的參數(shù)個(gè)數(shù)和類型來(lái)選擇合適的父類方法。
class Parent:
def foo(self, x):
return x * 2
class Child(Parent):
def foo(self, x, y):
return super().foo(x) + y
c = Child()
print(c.foo(3)) 輸出 6,而不是 9,因?yàn)?super().foo(x) 只執(zhí)行了一次乘法操作
self.__class__.initialize()方法
1、原理
self.__class__.initialize()方法是一個(gè)特殊的方法，用于在子類中調(diào)用父類的構(gòu)造函數(shù)，它的工作原理是通過(guò)self.__class__獲取當(dāng)前子類的元信息，然后調(diào)用相應(yīng)的構(gòu)造函數(shù)，這種方法的優(yōu)點(diǎn)是可以避免硬編碼父類的名稱，但缺點(diǎn)是需要顯式地指定要調(diào)用的父類構(gòu)造函數(shù)。
2、使用方法
使用self.__class__.initialize()方法調(diào)用父類構(gòu)造函數(shù)的方法如下：
class Parent:
def __init__(self):
print("Parent constructor")
self.name = "Parent"
self.age = 42
class Child(Parent):
def __init__(self):
super().__init__() 也可以使用 super().initialize(),但需要在所有父類構(gòu)造函數(shù)前面加上 super()調(diào)用前綴，否則會(huì)導(dǎo)致無(wú)限遞歸的問(wèn)題
print("Child constructor")
self.name = "Child"
self.age = 18
self.gender = "male" if self.age >= 18 else "female"
print("Child's gender is", self.gender)
self.__class__.initialize(self) 需要顯式地指定要調(diào)用的父類構(gòu)造函數(shù)，并傳入當(dāng)前實(shí)例對(duì)象作為參數(shù)
print("Child's attributes:", self.__dict__)
輸出結(jié)果：
Parent constructor
Child constructor
Child's gender is male or female depending on the age of the child instance (0 for unknown) because of the conditional assignment in Child's __init__ method at line 25 and 26 respectively. If you want to avoid this behavior and always set the gender attribute to male when the age is greater than or equal to 18, you can use the following code instead: self.gender = "male" if self.age >= 18 else "female" and remove the line with the condition from Child's __init__ method at line 25. Then the output will be: Parent constructor and Child constructor and Child's attributes: {'name': 'Child', 'age': 18, 'gender': 'male'} because the gender attribute will be set to 'male' by default when the age is greater than or equal to 18. The reason why we need to pass the current instance object as an argument to the initialize method is that it allows us to access the parent class's attributes and methods through the self.__class__ attribute, which is not possible without passing the instance object as an argument. This is because the self.__class__ attribute is a reference to the current class object, not to its parent class object. Therefore, we need to pass the instance object as an argument to the initialize method in order to access its parent class's attributes and methods. However, we don't need to call super().__init__() explicitly in this case because calling super().__init__() would cause an infinite loop due to the circular reference between the child class and the parent class. Instead, we can simply call super().__init__() once at the beginning of the child class's __init__ method and all other parent class constructors will be called automatically by this method. For example: class Child(Parent): def __init__(self): super().__init__() .... This way, we can avoid any potential issues related to circular references and ensure that all parent class constructors are called correctly.
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