class UserSerializer ReprSerializerMixin serializers ModelSerializer c

class UserSerializer(ReprSerializerMixin, serializers.ModelSerializer):
    class Meta:
        model = User
        fields = ('id', 'first_name', 'last_name',  'full_name', 'avatar_default', 'avatar_40', 'avatar_80',
                  'is_active')

    full_name = serializers.CharField(source='get_full_name', read_only=True)
    avatar_40 = serializers.SerializerMethodField()
    avatar_default = serializers.SerializerMethodField()
    avatar_80 = serializers.SerializerMethodField()

    is_active = serializers.BooleanField(read_only=True)

    def get_avatar_40(self, obj):
        return obj.get_avatar_url(40)

    def get_avatar_80(self, obj):
        return obj.get_avatar_url(80)

    def get_avatar_default(self, obj):
        return obj.get_avatar_url(settings.AVATAR_DEFAULT_SIZE)

    def validate_email(self, email):
        email = User.objects.normalize_email(email)
        existing = User.objects.all()
        if self.instance:
            existing = existing.exclude(id=self.instance.id)
        existing = existing.filter(is_active=True, email__iexact=email)
        if self.instance and self.instance.pk:
            existing = existing.exclude(pk=self.instance.pk)
        if existing.exists():
            raise serializers.ValidationError("Email already taken by another user.")

        return email