How to use class attribute in its instance method in Django?

I want to use variation attribute inside to_representation function in serializers.py. When I tried to implement it an error occured. I think I still don't understand the fundamental of Python class.
Here's my serializers.py:

class MarketSerializer(serializers.ModelSerializer):
    regions = serializers.PrimaryKeyRelatedField(many=True, queryset=Region.objects.all())
    languages = serializers.PrimaryKeyRelatedField(many=True, queryset=Language.objects.all())
    variation = serializers.SerializerMethodField('get_product_variations')

    class Meta:
        model = Market
        fields = ['id', 'regions', 'languages', 'name', 'status', 'variation']
        depth = 1

    @staticmethod
    def get_product_variations(self):
        return Product.objects.filter(distributor__region__market=self).distinct().count()

    def to_representation(self, instance):
        if self.context['request'].method == 'GET':
            regions = RegionSerializer(instance.regions, many=True).data
            languages = LanguageSerializer(instance.languages, many=True).data

            data = {
                'id': instance.id,
                'regions': regions,
                'languages': languages,
                'name': instance.name,
                'status': instance.status,
                'variation': self.variation,
            }
            return data
        return Serializer.to_representation(self, instance)

'variation': self.variation gives me this error on browsable API:

> AttributeError at /api/markets/
> 'MarketSerializer' object has no attribute 'variation'

While 'variation': MarketSerializer.variation and 'variation': self.__class__.variation give me this error:
> AttributeError at /api/markets/
> type object 'MarketSerializer' has no attribute 'variation'

Edit
'variation': variation gives me this error:

> NameError at /api/markets/
> name 'variation' is not defined

I am not sure how this suppose to work:

@staticmethod
def get_product_variations(self):
    return Product.objects.filter(distributor__region__market=self).distinct().count()

Because, in serializer method field, the method should be like this:

def get_product_variations(self, obj):
    # not a static method
    return Product.objects.filter(distributor__region__market=obj).distinct().count()

Similarly, you can use that method in to_represent method:

def to_representation(self, instance):
  ...
  data = {
            'id': instance.id,
            'regions': regions,
            'languages': languages,
            'name': instance.name,
            'status': instance.status,
            'variation': self.get_product_variations(instance),
        }
 ...

Or better:

def to_representation(self, instance):
      data = super().to_representation(instance)
      if self.context['request'].method == 'GET':
            data['regions'] = RegionSerializer(instance.regions, many=True).data
            data['languages'] = LanguageSerializer(instance.languages, many=True).data
      return data

Since you are trying to access the outer class instance from an inner class, use factory-method to build Inner instance and pass Outer instance to it.
We can not guarantee the existence of an outer class when you create an instance of the inner class

class MarketSerializer(object):
    variation = 'h'

    def MarketSerializer(self):
        return MarketSerializer.Meta(self)

    class Meta(object):
        def __init__(self, market_serializer_instance):
            self.market_serializer_instance = market_serializer_instance

        def inner_method(self):
            print(self.market_serializer_instance.variation)