How do you define a specific ordering in Django QuerySets?

Specifically, if I have a QuerySet like so: ['a10', 'a1', 'a2'].

Regular order (using Whatever.objects.order_by('someField')) will give me ['a1', 'a10', 'a2'], while I am looking for: ['a1', 'a2', 'a10'].

What is the proper way to define my own ordering technique?

python django django-models
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