Django models & Python class attributes

Question

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

from django.db import models

class Poll(models.Model):
    question = models.CharField(ma         


        

Answer 1

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)

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

Answer 2

A class instance has a namespace implemented as a dictionary which is the first place in which attribute references are searched.

http://docs.python.org/reference/datamodel.html

Answer 3

In Python, a class attribute is always also an instance attribute:

class C(object):
    a = 1
    def show_a(self):
        print self.a # <- works

But in django it is further complicated by the fact that Model classes have special metaclasses, so be careful to your assumptions!

Answer 4

It's done with metaclasses - very clever stuff. I'd recommend Marty Alchin's excellent book Pro Django if you want to learn more.