title: Django rest framework add dict to serializer
body: <p>This is my serializers.py:</p>
  
  <pre><code>class SysUserSerializer(serializers.ModelSerializer):
      pk = serializers.IntegerField(read_only=True)
      login_id = serializers.CharField(required=False)
      name = serializers.CharField(required=False)
  
      class Meta:
          model = SysUser
          fields = ('pk','login_id','name')
  </code></pre>
  
  <p>This is my views.py:</p>
  
  <pre><code>class GetUserDetail(APIView):
      def get(self, request, format=None):
          sysuser = SysUser.objects.get(id=1)
          serializer = SysUserSerializer(sysuser)
          serializer.data['gender'] = 'male' # i don't think this line is working
          return Response(serializer.data, status=200)
  </code></pre>
  
  <p>But i get this response:</p>
  
  <pre><code>{"pk": 1, "login_id": "john77", "name": "John"}
  </code></pre>
  
  <p>I want the response like this:</p>
  
  <pre><code>{"pk": 1, "login_id": "john77", "name": "John", "gender": "male"}
  </code></pre>
  
  <p>How it can be done? is it possible to do so?</p>