[Django]-"Cannot filter a query once a slice has been taken"

I don’t know how to solve your problem (seems you have already) but I think this is why you’re getting the error: https://docs.djangoproject.com/en/1.4/ref/models/querysets/

“Slicing. As explained in Limiting QuerySets, a QuerySet can be
sliced, using Python’s array-slicing syntax. Slicing an unevaluated
QuerySet usually returns another unevaluated QuerySet, but Django will
execute the database query if you use the “step” parameter of slice
syntax, and will return a list. Slicing a QuerySet that has been
evaluated (partially or fully) also returns a list.”

I guess you are forcing the queryset to be evaluated using the slice, so that further filtering results in an error?

This is what eventually worked for me

_latest_shipment_ids = [address.id for address in Address.objects.filter(shipment_pickup__user=user).order_by('-shipment_pickup__created')[:5]]
copy_pickup_address = ModelChoiceField(
    required=False,
    queryset=Address.objects.filter(
        shipment_pickup__user=user,
        id__in=_latest_shipment_ids
    )
)

I’ve gotten around a similar error by pulling my query-set out side of the code and then filtering it on the next line.

query = Address.objects.filter(shipment_pickup__user=user).order_by('-shipment_pickup__created')
copy_pickup_address = ModelChoiceField(required=False, queryset=query[:5])

Not sure if that’ll work with your code.