Question

在Python中，如何从超类中创建子类？

Answer 1

# Initialize using Parent
#
class MySubClass(MySuperClass):
    def __init__(self):
        MySuperClass.__init__(self)

或者更好的是，使用Python的内置函数super()（请参阅Python 2 / Python 3文档）可能是一种稍微好一点的调用父项的方法用于初始化：

# Better initialize using Parent (less redundant).
#
class MySubClassBetter(MySuperClass):
    def __init__(self):
        super(MySubClassBetter, self).__init__()

或者，与上面完全相同，除了使用super()的零参数形式，它仅适用于类定义：

class MySubClassBetter(MySuperClass):
    def __init__(self):
        super().__init__()

Answer 2

一个英雄的小例子：

class SuperHero(object): #superclass, inherits from default object
    def getName(self):
        raise NotImplementedError #you want to override this on the child classes

class SuperMan(SuperHero): #subclass, inherits from SuperHero
    def getName(self):
        return "Clark Kent"

class SuperManII(SuperHero): #another subclass
    def getName(self):
       return "Clark Kent, Jr."

if __name__ == "__main__":
    sm = SuperMan()
    print sm.getName()
    sm2 = SuperManII()
    print sm2.getName()

Answer 3

class MySubClass(MySuperClass):
    def __init__(self):
        MySuperClass.__init__(self)

        # <the rest of your custom initialization code goes here>

python文档中的section on inheritance更详细地解释了它

Answer 4

class Class1(object):
    pass

class Class2(Class1):
    pass

第2类是第1类的子类

Answer 5

在上面的答案中，super初始化时没有任何（关键字）参数。但是，通常情况下，您希望这样做，并传递一些＆＃39; custom＆＃39;你自己的论点。下面是一个说明此用例的示例：

class SortedList(list):
    def __init__(self, *args, reverse=False, **kwargs):
        super().__init__(*args, **kwargs)       # Initialize the super class
        self.reverse = reverse
        self.sort(reverse=self.reverse)         # Do additional things with the custom keyword arguments

这是list的子类，在初始化时，会立即按reverse关键字参数指定的方向排序，如下面的测试所示：

import pytest

def test_1():
    assert SortedList([5, 2, 3]) == [2, 3, 5]

def test_2():
    SortedList([5, 2, 3], reverse=True) == [5, 3, 2]

def test_3():
    with pytest.raises(TypeError):
        sorted_list = SortedList([5, 2, 3], True)   # This doesn't work because 'reverse' must be passed as a keyword argument

if __name__ == "__main__":
    pytest.main([__file__])

由于将*args传递给super，因此可以初始化列表并使用项目填充，而不是仅为空。（请注意，reverse是符合关键字的参数，符合PEP 3102）。

Answer 6

还有另一种方法可以使用函数type()动态地在python中创建子类：

SubClass = type('SubClass', (BaseClass,), {'set_x': set_x})  # Methods can be set, including __init__()

使用元类时，通常需要使用此方法。当你想做一些较低级别的自动化时，这会改变python创建类的方式。很可能你不需要这样做，但是当你这样做时，你已经知道你在做什么了。

Answer 7

class Subclass (SuperClass):
      # Subclass stuff here

Answer 8

您使用：

class DerivedClassName(BaseClassName):

有关详细信息，请参阅Python docs, section 9.5。

Answer 9

class Mammal(object): 
#mammal stuff

class Dog(Mammal): 
#doggie stuff

Answer 10

class BankAccount:

  def __init__(self, balance=0):
    self.balance = int(balance)

  def checkBalance(self): ## Checking opening balance....
    return self.balance

  def deposit(self, deposit_amount=1000): ## takes in cash deposit amount and updates the balance accordingly.
    self.deposit_amount = deposit_amount
    self.balance += deposit_amount
    return self.balance

  def withdraw(self, withdraw_amount=500): ## takes in cash withdrawal amount and updates the balance accordingly
    if self.balance < withdraw_amount: ## if amount is greater than balance return `"invalid transaction"`
        return 'invalid transaction'
    else:
      self.balance -= withdraw_amount
      return self.balance


class MinimumBalanceAccount(BankAccount): #subclass MinimumBalanceAccount of the BankAccount class

    def __init__(self,balance=0, minimum_balance=500):
        BankAccount.__init__(self, balance=0)
        self.minimum_balance = minimum_balance
        self.balance = balance - minimum_balance
        #print "Subclass MinimumBalanceAccount of the BankAccount class created!"

    def MinimumBalance(self):
        return self.minimum_balance

c = BankAccount()
print(c.deposit(50))
print(c.withdraw(10))

b = MinimumBalanceAccount(100, 50)
print(b.deposit(50))
print(b.withdraw(10))
print(b.MinimumBalance())

Answer 11

Python中的子类化完成如下：

class WindowElement:
    def print(self):
        pass

class Button(WindowElement):
    def print(self):
        pass

这是关于Python的tutorial，它还包含类和子类。

Python：如何从超类创建子类？

11 个答案: