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POWhy can't I use __getattr__ with Django models?
 

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  1. POWhy can't I use __getattr__ with Django models?
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    <p>I've seen examples online of people using <code>__getattr__</code> with Django models, but whenever I try I get errors. (Django 1.2.3)</p> <p>I don't have any problems when I am using <code>__getattr__</code> on normal objects. For example:</p> <pre><code>class Post(object): def __getattr__(self, name): return 42 </code></pre> <p>Works just fine...</p> <blockquote> <pre><code> &gt;&gt;&gt; from blog.models import Post &gt;&gt;&gt; p = Post() &gt;&gt;&gt; p.random 42 </code></pre> </blockquote> <p>Now when I try it with a Django model:</p> <pre><code>from django.db import models class Post(models.Model): def __getattr__(self, name): return 42 </code></pre> <p>And test it on on the interpreter:</p> <blockquote> <pre><code> &gt;&gt;&gt; from blog.models import Post &gt;&gt;&gt; p = Post() ERROR: An unexpected error occurred while tokenizing input The </code></pre> <p>following traceback may be corrupted or invalid The error message is: ('EOF in multi-line statement', (6, 0))</p> <p>--------------------------------------------------------------------------- TypeError<br> Traceback (most recent call last)</p> <p>/Users/josh/project/ in ()</p> <p>/Users/josh/project/lib/python2.6/site-packages/django/db/models/base.pyc in <strong>init</strong>(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.<strong>class</strong>, instance=self) 341 342 def <strong>repr</strong>(self):</p> <p>/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</p> <p>/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</p> <p>TypeError: 'int' object is not callable</p> </blockquote> <p>Can someone explain what is going on?</p> <hr> <p>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:</p> <pre><code>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... </code></pre> <p>While I <em>could</em> 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.</p>
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    1. COis that really "return self.post.name"? It should be "return getattr(self.post, name)"
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      1. USAndrew Dalke
    2. COIndeed, that is what the code should be
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