Django 模型与Python 类属性

问题描述

django 网站上的教程显示了模型的以下代码:

The tutorial on the django website shows this code for the models:

from django.db import models

class Poll(models.Model):
    question = models.CharField(max_length=200)
    pub_date = models.DateTimeField('date published')

class Choice(models.Model):
    poll = models.ForeignKey(Poll)
    choice = models.CharField(max_length=200)
    votes = models.IntegerField()

现在，这些属性中的每一个都是类属性，对吧?因此，该类的所有实例都应共享相同的属性.稍后，他们展示了这段代码:

Now, each of those attribute, is a class attribute, right? So, the same attribute should be shared by all instances of the class. A bit later, they present this code:

class Poll(models.Model):
    # ...
    def __unicode__(self):
        return self.question

class Choice(models.Model):
    # ...
    def __unicode__(self):
        return self.choice

它们是如何从类属性转变为实例属性的?我是不是把类属性弄错了?

How did they turn from class attributes into instance attributes? Did I get class attributes wrong?

推荐答案

看看django/db/models.py下的Model类.在那里，类属性通过类似的方式转换为实例属性

Have a look at the Model class under django/db/models.py. There the class attributes are turned to instance attributes via something like

setattr(self, field.attname, val)

人们可能会推荐整个文件(ModelBase 和 Model 类)作为元类的优秀实践示例.

One might recommend the whole file (ModelBase and Model class) as an excellent hands-on example on metaclasses.