class Product(models.Model):
    upload_path = 'media/product'
    image = models.ImageField(upload_to=upload_path, null=True, blank=True)
    image_url = models.URLField(null=True, blank=True)

    def save(self, *args, **kwargs):
        if self.image_url:
            import urllib, os
            from urlparse import urlparse
            file_save_dir = upload_path
            filename = urlparse(self.image_url).path.split('/')[-1]
            urllib.urlretrieve(self.image_url, os.path.join(file_save_dir, filename))
            self.image = os.path.join(file_save_dir, filename)
            self.image_url = ''
        super(Product, self).save()