DRF overwriting __init__ for Serializer to conditionally add fields.

serializers.py

from rest_framework.serializers import HyperlinkedModelSerializer
from dry_rest_permissions.generics import DRYPermissionsField

from .models import CustomUser


class CustomUserSerializer(HyperlinkedModelSerializer):
    permissions = DRYPermissionsField(additional_actions=["activate", "deactivate"])

    class Meta:
        model = CustomUser
        fields = ("url", "id", "name", "email", "permissions", "role", "is_active")
        # non admin should't be able to update role and is_active
        read_only_fields = ["role", "is_active"]

class ForAdminCustomUserSerializer(CustomUserSerializer):

    class Meta:
        model = CustomUser
        fields = ("url", "id", "name", "email", "permissions", "role", "is_active")



    def __init__(self, *args, **kwargs):
        super(CustomUserSerializer, self).__init__(*args, **kwargs)
        # get the request from parent serializer's context
        request_obj = self.context.get('request')
        # add extra fields if user is admin
        if  request_obj.user.role == 'ADMIN':
            self.Meta.fields = list(self.Meta.fields)
            self.Meta.fields.extend(["role", "is_active"])