old_contents: import models
  import django_filters
  
  from core.custom_filters import EmptyFilter, DateRangeFilter
  from core.widgets import DateRangeWidget
  
  
  class SourceFilter(EmptyFilter):
      publisher = django_filters.CharFilter(lookup_type='name__icontains')
      seed__url = django_filters.CharFilter(lookup_type='icontains')
  
      created = DateRangeFilter()
  
      class Meta:
          model = models.Source
          fields = ('name', 'owner', 'seed__url', 'publisher', 'state',
                    'category', 'sub_category', 'suggested_by', 'created',
                    'last_changed')
  
new_contents: import models
  import django_filters
  
  from core.custom_filters import EmptyFilter, DateRangeFilter
  from core.widgets import DateRangeWidget
  
  
  class SourceFilter(EmptyFilter):
      publisher = django_filters.CharFilter(lookup_type='name__icontains')
      seed__url = django_filters.CharFilter(lookup_type='icontains')
  
      created = DateRangeFilter()
      last_changed = DateRangeFilter()
  
      class Meta:
          model = models.Source
          fields = ('name', 'owner', 'seed__url', 'publisher', 'state',
                    'category', 'sub_category', 'suggested_by', 'created',
                    'last_changed')
  
subject: use DateRangeFilter for last_changed field