Why can't I use __getattr__ with Django models?
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Joshmaker
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Published on 2011-01-07T21:12:35Z
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2011/01/10
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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.
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