Django Admin Natural Sort QuerySet Example (answer to https://stackoverflow.com/questions/50689359/django-1-11-natural-sort-queryset/59220344#59220344)

admin.py

from django.contrib.admin import ModelAdmin, register, SimpleListFilter
from django.db.models.functions import Length, StrIndex, Substr, NullIf, Coalesce
from django.db.models import Value as V

from .models import Item


class AlphanumericSignatureFilter(SimpleListFilter):
    title = 'Signature (alphanumeric)'
    parameter_name = 'signature_alphanumeric'

    def lookups(self, request, model_admin):
        return (
            ('signature', 'Signature (alphanumeric)'),
        )

    def queryset(self, request, queryset):
        if self.value() == 'signature':
            return queryset.order_by(
                Coalesce(Substr('signature', V(0), NullIf(StrIndex('signature', V(' ')), V(0))), 'signature'),
                Length('signature'),
                'signature'
            )


@register(Item)
class Item(ModelAdmin):
    list_filter = [AlphanumericSignatureFilter]

models.py

from django.db import models


class Item(models.Model):
    signature = models.CharField('Signatur', max_length=50)

    def __str__(self):
        return self.signature