Why can't I use __getattr__ with Django models?
- by Joshmaker
I've seen examples online of people using __getattr__ with Django models, but whenever I try I get errors. (Django 1.2.3)
I don't have any problems when I am using __getattr__ on normal objects. For example:
class Post(object):
def __getattr__(self, name):
return 42
Works just fine...
>>> from blog.models import Post
>>> p = Post()
>>> p.random
42
Now when I try it with a Django model:
from django.db import models
class Post(models.Model):
def __getattr__(self, name):
return 42
And test it on on the interpreter:
>>> from blog.models import Post
>>> p = Post()
ERROR: An unexpected error occurred while tokenizing input The
following traceback may be corrupted
or invalid The error message is: ('EOF
in multi-line statement', (6, 0))
--------------------------------------------------------------------------- TypeError
Traceback (most recent call last)
/Users/josh/project/
in ()
/Users/josh/project/lib/python2.6/site-packages/django/db/models/base.pyc
in init(self, *args, **kwargs)
338 if kwargs:
339 raise TypeError("'%s' is an invalid keyword
argument for this function" %
kwargs.keys()[0])
-- 340 signals.post_init.send(sender=self.class,
instance=self)
341
342 def repr(self):
/Users/josh/project/lib/python2.6/site-packages/django/dispatch/dispatcher.pyc
in send(self, sender, **named)
160
161 for receiver in self._live_receivers(_make_id(sender)):
-- 162 response = receiver(signal=self, sender=sender,
**named)
163 responses.append((receiver, response))
164 return responses
/Users/josh/project/python2.6/site-packages/photologue/models.pyc
in add_methods(sender, instance,
signal, *args, **kwargs)
728 """
729 if hasattr(instance, 'add_accessor_methods'):
-- 730 instance.add_accessor_methods()
731
732 # connect the add_accessor_methods function to the
post_init signal
TypeError: 'int' object is not
callable
Can someone explain what is going on?
EDIT: I may have been too abstract in the examples, here is some code that is closer to what I actually would use on the website:
class Post(models.Model):
title = models.CharField(max_length=255)
slug = models.SlugField()
date_published = models.DateTimeField()
content = RichTextField('Content', blank=True, null=True)
# Etc...
Class CuratedPost(models.Model):
post = models.ForeignKey('Post')
position = models.PositiveSmallIntegerField()
def __getattr__(self, name):
''' If the user tries to access a property of the CuratedPost, return the property of the Post instead... '''
return self.post.name
# Etc...
While I could create a property for each attribute of the Post class, that would lead to a lot of code duplication. Further more, that would mean anytime I add or edit a attribute of the Post class I would have to remember to make the same change to the CuratedPost class, which seems like a recipe for code rot.
