django expressionwrapper example

from django.db.models import F, Avg, Value, FloatField, ExpressionWrapper
from django.db.models.functions.comparison import NullIf

context['stock_margin'] = context['top_stock'].annotate(
    Avg_purchase = ExpressionWrapper(
        F('total_puchase') / NullIf(F('quantity_purchase'), 0),
        output_field=FloatField()
    ),
    Avg_sales = ExpressionWrapper(
        F('total') / NullIf(F('quantity'), 0),
        output_field=FloatField()
    )
)