Question

I’m working my way through a tutorial on how to up load images, and I’m at a complete loss on the method this guy uses to generate a thumbnail for submitted pictures

Here’s a trimmed down chunk of his code:

import os.path
from PIL import Image as PImage
from settings import MEDIA_ROOT
from tempfile import *

class Image(models.Model):
    image = models.FileField(upload_to="images/")
    thumbnail = models.ImageField(upload_to="images/", blank=True, null=True)

    def save(self, *args, **kwargs):
        super(Image, self).save(*args, **kwargs)
        im = PImage.open(pjoin(MEDIA_ROOT, self.image.name))

        fn, ext = os.path.splitext(self.image.name)
        im.thumbnail((128,128), PImage.ANTIALIAS)
        thumb_fn = fn + "-thumb" + ext
        tf = NamedTemporaryFile()
        im.save(tf.name, "JPEG")
        self.thumbnail.save(thumb_fn, File(open(tf.name)), save=False)
        tf.close()

        super(Image, self).save(*args, ** kwargs)

so my specific questions about this are:

1. Any reason he uses FileField for the image and ImageField for the thumbnail?
2. From what I understand, super(Image, self).save(*args, **kwargs) saves the model. but why does he call it again at the end?
3. Then I don’t really understand the role NamedTemporaryFile() plays and what exactly happens when self.thumbnail.save(thumb_fn, File(open(tf.name)), save=False) is called

Answer 1

1. I would use ImageField for the main image as well. ImageField
   inherits from FileField but ensures that only image files can be
   uploaded, among other things:
   https://docs.djangoproject.com/en/dev/ref/models/fields/#django.db.models.ImageField

2. First save() saves the image object to DB, but it has (supposedly) no thumbnail set yet. Second save() call updates the DB with the changes made to the instance (thumbnail added).

   He sets the thumbnail field with
   self.thumbnail.save(thumb_fn, File(open(tf.name)), save=False),
   but that only saves the thumbnail to a file in the appropriate location and fills in the instance’s thumbnail attr with the path to it. You then need to call save() on the Image instance again to update the changes on the object to DB (thumbnail added).

3. The code is reading the uploaded main image file and with that image in memory composes the thumbnail from it (in memory, it does not exist as a file yet).

   But that thumbnail needs to be saved on a file so it can be used with Django ImageFile (that expects an uploaded file temporarily saved on disk) and that is what he is doing with NamedTemporaryFile.

   The ImageFile instance takes then care of copying that file to the appropriate location (set with your MEDIA_ROOT setting + the upload_to argument).