澄清/何时/何地在 django/python 中使用 super [英] clarification/when/where to use super in django/python

问题描述

实际上我们知道 super 用于查找父类"并返回其对象，类似于/使用 self.__class__.__mro__

Actually we know super is used to find the "parent class" and return its object, something like/using self.__class__.__mro__

让我感到困惑的是什么时候使用它?

假设我们有一个示例模型代码如下

Suppose we have a Example model code as below

version_1

class Example(models.Model):
    name = models.CharField()
    age  = models.IntegerField()

    def save(self, **args, **kwargs):
        obj = super(Example, self).save(self, **args, **kwargs)
        obj.name = "name changed"
        obj.age = "age changed"
        return obj

version_2

class Example(models.Model):
    name = models.CharField()
    age  = models.IntegerField()

    def save(self, **args, **kwargs):
        self.name = "name changed"
        self.age = "age changed"
        obj = super(Example, self).save(self, **args, **kwargs)
        return obj

所以我们可以在上面观察

so as we can observe above

在version_1中，我首先调用了super并对字段进行了修改并返回了obj

In version_1 I have called super first and done modifications to fields and returned the obj

在 version_2 中，我修改了字段，然后调用了 super 并返回了 obj

In version_2 I had modified the fields and after that called super and returned obj

那么在修改字段之前和之后调用super会发生什么?

So what happens when super is called before and after modification of fields?

最后我想知道/确认的是

Finally what i want to know/confirm is

• 在 Django 表单/模型中究竟在哪里/为什么使用 super.
• 在 django/python 中使用它们的确切概念是什么(如果我理解错了).

推荐答案

您的 Example 类是 Model 的子类.这意味着，Example 继承了 Model 的所有函数.

Your Example class is a subclass of Model. That means, that Example inherits all functions from Model.

请看以下内容:

class Example():
    pass

example = Example()
#let's try to save it
example.save()

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: Example instance has no attribute 'save'

现在有了继承.

class Parent():
    def save(*args, **kwargs):
        print "saving now"

class Example(Parent):
    pass

example = Example()
#since Example has no save method, it inherits the Parent's save method.
example.save()
"saving now"

如果在 Example 类中覆盖 save() 方法，则不会调用 Parent 的 save 方法.

If you override the save() method in your Example class, the Parent's save method will not be called.

   class Example(Parent):
        def save(self, *args, **kwargs):
            print "i know how to save on my own now"

   example = Example()
   example.save()
   "i know how to save on my own now"

如果你选择调用 super，你就是在调用 Parent 的 save 函数以及你自己的 save() 实现.

If you choose to call super, you are calling the Parent's save function together with your own implementation of save().

   class Example(Parent):
         def save(self, *args, **kwargs):
              super(Example, self).save(*args, **kwargs)
              print "i know how to save on my own now"

   example = Example()
   example.save()
   "saving now" #from parent
   "i know how to save on my own" #from example

这同样适用于您继承的所有 djangos 类.实际上，实现要复杂得多.您可以在 github 上查看模型定义.

The same applies to all of djangos classes you inherit from. In fact, the implementation is more complex. You can take a look at the Model definition here on github.

如果您感到兴奋，可以通过这个谈话

If you feel thrilled, you can dive into the django ORM with this talk

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