Python从构造函数继承

Question

person.py

class Person:
   """---A class representing a person---"""
   # Person constructor
   def __init__(self,n,a): 
       self.full_name = n
       self.age = a
class Student(Person):
    # Student constructor   
    def __init__(self,n,a,s):
       Person.__init__(self,n,a)
       self.school = s

driver.py

from person import *
    a = Student("Alice", 19, "Univ")

它抛出TypeError: __init__() takes 3 positional arguments but 4 were given 我尝试将 Student 类更改为以下内容：

class Student(Person):
        # Student constructor   
        def __init__(self,n,a,s):
           super().__init__(n,a)
           self.school = s

错误依然存在。

为什么会这样？是否需要 super() 关键字才能添加新属性？

编辑：问题解决了。呈现这种奇怪行为的源代码中存在缩进问题，因此应该关闭问题。

Answer 1

这一行：

Person.__init__(self,n,a)

是问题所在。回想一下，方法会自动传递对其自身的引用，因此您只需传递第二个。

这也有一个成熟的模式：

class Person
    def __init__(self, name, age):
        self.name = name
        self.age = age

class Student(Person):
    def __init__(self, school, *args):
        super().__init__(*args)
        self.school = school

student = Student('Washington Elementary', "Johnny Go'gettem", 10)

尽管请注意，只需在Student.__init__ 内的Person.__init__ 调用中删除对self 的引用就足够了。

---

请注意，您可以使用几个在某些情况下变得非常有用的装饰器来覆盖默认方法行为。在这里都不适用，只是一点知识来逗你的大脑：

def SomeClass:
    attr = "class-scoped"

    def __init__(self):
        self.attr = "instance-scoped"

    def some_method(self):
        return self.attr == "instance-scoped"

    @classmethod
    def some_classmethod(cls):
        return cls.attr == "class-scoped"

    @staticmethod
    def some_staticmethod():
        return "I'm not given a \"self\" parameter at all!"

classmethods 作为替代构造函数特别有用

class Person:
    def __init__(self, name, age):
        self.name = name
        self.age = age

    @classmethod
    def from_tuple(cls, tup) -> "Person":
        """Expects a tuple of (name, age) and constructs a Person"""
        name, age = tup
        return cls(name, age)

    @classmethod
    def from_dict(cls, dct) -> "Person":
        """Expects a dictionary with keys "name" and "age" and constructs a Person"""
        try:
            name = dct['name']
            age = dct['age']
        except KeyError:
            raise ValueError(f"Dictionary {dct} does not have required keys 'name' and 'age'")
        else:
            return cls(name, age)