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POPreferred pythonic way to associate upload_to function with model class?
 

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  1. POPreferred pythonic way to associate upload_to function with model class?
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    <p>I have a class with a <a href="https://docs.djangoproject.com/en/dev/ref/models/fields/#imagefield" rel="nofollow noreferrer">Django ImageField</a> and I have been struggling to decide between two alternatives for storing that field's <code>upload_to</code> function. The first approach is pretty straightforward. The function is defined on the module level (c.f. <a href="https://stackoverflow.com/a/1190866/790075">https://stackoverflow.com/a/1190866/790075</a>, <a href="https://stackoverflow.com/a/3091864/790075">https://stackoverflow.com/a/3091864/790075</a>):</p> <pre><code>def get_car_photo_file_path(instance, filename): ext = filename.split('.')[-1] filename = "%s.%s" % (uuid.uuid4(), ext) # chance of collision &lt;1e-50 return os.path.join('uploads/cars/photos', filename) class CarPhoto(models.Model): photo = models.ImageField(upload_to=get_car_photo_file_path) </code></pre> <p>This is simple and easy to understand, but pollutes the module scope by adding a function that is really only pertinent to the CarPhoto class.</p> <p>In the second approach, I use the callable-class pattern to associate the function more closely with the CarPhoto class. This moves the <code>upload_to</code> function out of module scope but feels unnecessarily complicated.</p> <pre><code>class CarPhoto(models.Model): class getCarPhotoFilePath(): # Either use this pattern or associate function with module instead of this class def __call__(self, instance, filename): ext = filename.split('.')[-1] filename = "%s.%s" % (uuid.uuid4(), ext) # chance of collision &lt;1e-50 return os.path.join('uploads/cars/photos', filename) photo = models.ImageField(upload_to=getCarPhotoFilePath()) </code></pre> <p>I have seen suggestions for using the <code>@staticmethod</code> and <code>@classmethod</code> decorators (c.f. <a href="https://stackoverflow.com/a/9264153/790075">https://stackoverflow.com/a/9264153/790075</a>), but I find that when I do this the function never executes and the filename ends up looking like: <code>/path/to/file/&lt;classmethod object&gt;</code>, with the method object embedded in the file path, which is certainly not intended!</p> <p>Which of these is the preferred pattern? Is there a better way?</p>
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    1. COBTW you can avoid defining a function / method / class altogether and turn your `get_car_photo_file_path`into an inline lambda right inside `ImageField` invocation. But this probably be totally unreadable.
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