Override imported class variables - django/python

Question

I need to override variables (or pass dynamic data) to imported class.

filters.py

import django_filters
from .models import Gate, Tram, OperationArea, Bogie
from distutils.util import strtobool
from django import forms


class GateFilter(django_filters.FilterSet):

    # Prepare dynamic lists with choices
    tram_list = [(id, number) for id, number in Tram.objects.all().values_list('id', 'number')]
    bogie_list = [(id, number) for id, number in Bogie.objects.all().values_list('id', 'number')]
    area_list = [(id, area) for id, area in OperationArea.objects.all().values_list('id', 'area')]
    # Generate fields
    tram = django_filters.MultipleChoiceFilter(choices=tram_list, label=u'Tramwaj')
    car = django_filters.MultipleChoiceFilter(choices=Gate.CAR_SYMBOLS, label=u'Człon')
    bogie = django_filters.MultipleChoiceFilter(choices=bogie_list, label=u'Wózek')
    bogie_type = django_filters.MultipleChoiceFilter(choices=Gate.BOGIE_TYPES, label=u'Typ wózka')
    area = django_filters.MultipleChoiceFilter(choices=area_list, label=u'Obszar')
    operation_no = django_filters.CharFilter(label=u'Numer operacji', widget=forms.TextInput(attrs={'size': '16px'}))
    status = django_filters.MultipleChoiceFilter(choices=Gate.GATE_STATUSES, label=u'Status')
    rating = django_filters.MultipleChoiceFilter(choices=Gate.GATE_GRADES, label=u'Ocena')

    class Meta:
        pass

views.py

from .filters import GateFilter

class GateListView(generic.ListView):

    queryset = None
    gate_type = None
    template_name = 'qapp/gate/list.html'
    context_object_name = 'gate_list'
    paginate_by = 20

    def get_queryset(self):
        # Type is stored in database as big-letter word, so 'bjc' != 'BJC'.
        if self.gate_type.upper() == 'BJW':
            ordering = ['bogie', 'bogie_type']
        else:
            ordering = ['tram', 'car']
        queryset = Gate.objects.filter(type=self.gate_type.upper()).order_by(*ordering)
        self.gate_list = GateFilter(self.request.GET, queryset=queryset)
        return self.gate_list.qs.distinct()

    def get_context_data(self, **kwargs):
        context = super(GateListView, self).get_context_data(**kwargs)
        # Return Gate.type to template.
        context['gate_type'] = self.gate_type
        # Return object (for generating form) to template.
        context['gate_list_filter'] = self.gate_list
        return context

As you can see, in the filters.py , the data for variables tram_list, bogie_list and area_list are dynamic (fetched from database).

But during importing this class to views.py, this data becomes static.

I tried to override this values:

• using @classmethod decorator in class GateFilter , and calling it before setting self.gate_list object,
• in views.py using GateFilter.tram_list (and the rest) notation,

No luck.

I can't use reload() function, due to import type ( from .filters import GateFilter ).

Currently for update lists in filters.py I need to rerun whole app. This is unacceptable for business logic of my app.

Answer 1

This is the wrong approach. Rather, you should be using the filters that are aware of querysets and that evaluate them when required: ModelChoiceFilter and ModelMultipleChoiceFilter.

class GateFilter(django_filters.FilterSet):
    team = django_filters.ModelMultipleChoiceFilter(queryset=Tram.objects.all())