themes/models.py

from django.db import models
from . import available_themes, default_theme
from PIL import Image


class Setting(models.Model):
    page_image = models.ImageField(
        upload_to='theme',
        default='theme/logo.png'
    )
    page_theme = models.CharField(
        max_length=64,
        choices=available_themes,
        default=default_theme
    )
    page_title = models.CharField(max_length=32, default='MyApp', blank=True)

    def save(self, *args, **kwargs):
        super().save(*args, **kwargs)

        img = Image.open(self.page_image.path)
        if img.height > 50:
            output_size = (int(img.width * 50 / img.height), 50)
            img.thumbnail(output_size)
            img.save(self.page_image.path)


class BottomBar(models.Model):
    name = models.CharField(max_length=64, blank=True)
    icon = models.ImageField(upload_to='theme', blank=True)
    url = models.URLField()
    left = models.BooleanField()
    sequence_number = models.SmallIntegerField(choices=[(1, '1'), (2, '2'), (3, '3'), (4, '4'), (5, '5')])

    def save(self, *args, **kwargs):
        super().save(*args, **kwargs)
        if self.icon:
            img = Image.open(self.icon.path)
            if img.height > 40:
                output_size = (int(img.width * 40 / img.height), 40)
                img.thumbnail(output_size)
                img.save(self.icon.path)