Question

我是Python新手。我有这段代码：

class SomeClass(OtherClass):
    name = "whatever"
    task = "nothing"

现在，我想创建一个子类，我可以像这样实例化它：

child = ChildClass(task = "sometask")
child.name #=> "whatever"
child.task #=> "sometask"
child2 = ChildClass()
child2.task #=> "nothing"

我该怎么做？

Answer 1

首先，您需要注意在SomeClass创建类变量，而不是实例变量

class SomeClass(object):
    def __init__(self, name = "whatever", task = "nothing"):
        self.name = name
        self.task = task

现在我们设计了一个类，它接受两个带默认值的关键字参数。因此，如果您未将值传递给其中任何一个，默认情况下whatever将分配给name，而nothing将分配给task。

class ChildClass(SomeClass):
    def __init__(self, name = "whatever", task = "nothing"):
        super(ChildClass, self).__init__(name, task)

child1 = ChildClass(task = "sometask")
print child1.name, child1.task
# whatever sometask
child2 = ChildClass()
print child2.name, child2.task
# whatever nothing

Answer 2

您需要覆盖其初始值设定项（有点像其他语言的构造函数）：

>>> class SomeClass:
...   name='whatever'
...   task='nothing'
...
>>> class ChildClass(SomeClass):
...   def __init__(self, name=None, task=None):
...     if name is not None:
...       self.name = name
...     if task is not None:
...       self.task = task
...
>>> child = ChildClass(task='sometask')
>>> child.name
'whatever'
>>> child.task
'sometask'
>>> child2 = ChildClass()
>>> child2.task
'nothing'

使用可选参数对python类进行子类化

2 个答案: