多个构造函数在python中，使用继承 [英] Multiple constructors in python, using inheritance

问题描述

我有一个类AbstractDataHandle，他的 init 方法和类Classifier。我想有两个构造函数在Classifier，Java like。一个继承自它的超类，一个全新的。

I have a class AbstractDataHandle, whith his init method, and a class Classifier. I would like to have two constructors in Classifier, Java like. One inherited from it`s superclass, and one brand new.

这将是类似的东西（但我打算保留两个构造函数）：

It would be something like (but i intend to "keep" the two constructors):

class AbstractDataHandle():
    def __init__(self, elements, attributes, labels):
        self._load(elements, attributes, labels)


class Classifier(AbstractDataHandle):
    def __init__(self, classifier="LinearSVC", proba=False):
        self._fit(classifier, proba)

我可以在一个类中有两个构造函数？
如果是，我可以从一个超类继承一个构造函数，并添加一个新的？

Can i have two constructors in one class? If yes, can i have a constructor inherited from a superclass, and add a new one?

提前感谢。

推荐答案

构造函数必须命名为 __ init __ 。并且，与Java不同，Python不允许通过它们的参数类型重载函数或方法。所以，如果你有两个构造函数，它们都将是相同的函数。

Constructors have to be named __init__. And, unlike Java, Python doesn't allow overloading functions or methods by the type of their arguments. So, if you had two constructors, they would both be the same function.

有几种方法。

使用 @classmethod 作为替代构造函数：

Use @classmethods as alternate constructors:

class Breakfast(object):
    @classmethod
    def from_eggs(cls, eggs):
        obj = cls()
        obj.spam, obj.eggs = 5, eggs
        return obj

    @classmethod
    def from_spam_and_eggs(cls, spam, eggs):
        obj = cls()
        obj.spam, obj.eggs = spam, eggs
        return obj

从标准库中是 datetime.datetime ，可以用 now ， fromtimestamp 或其他几个替代构造函数，除了默认。

A simple example from the standard library is datetime.datetime, which can be constructed with now, fromtimestamp, or a few other alternate constructors, besides the default.

使用默认值关键字 - 只是，和/或可变参数参数，使单个构造函数可以被称为不同的方式：

Use default-valued, keyword-only, and/or variable-argument parameters to make a single constructor that can be called different ways:

class Breakfast(object):
    def __init__(self, eggs=0, spam=5):
        self.spam, self.eggs = spam, eggs

int 就是一个例子：你可以从一个字符串和一个基础，或者从一个知道如何将自己转换为整数的参数创建它。

int is an example of this: You can create it from a string and a base, or from a single argument that knows how to convert itself to an integer.

创建具有不同构造函数的子类：

Create subclasses that each have different constructors:

class Breakfast(object):
    pass

class HealthyBreakfast(object):
    def __init__(self, spam):
        self.spam, self.eggs = spam, 0

class NormalBreakfast(object):
    def __init__(self, spam, eggs):
        self.spam, self.eggs = spam, eggs

---

在任何一种情况下，初始化。例如：

---

In any of these cases, you can factor out commonalities into a single "base" initializer. For example:

class Breakfast(object):
    def __init__(self, eggs, spam):
        self.spam, self.eggs = spam, eggs

class HealthyBreakfast(object):
    def __init__(self, spam):
        super(HealthyBreakfast, self).__init__(0, spam)

---

当然不会是可能有早餐没有垃圾邮件。

---

Of course in no case is it possible to have breakfast without spam.

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