title: Django Rest Framework How to update SerializerMethodField
body: <p>I have a serializer like this:</p>
  
  <pre><code>class PersonSerializer(serializers.ModelSerializer):
      gender = serializers.SerializerMethodField()
      bio = BioSerializer()
  
      class Meta:
          model = Person
          fields = UserSerializer.Meta.fields + ('gender', 'bio',)
  
      def get_gender(self, obj):
          return obj.get_gender_display()
  </code></pre>
  
  <p>I used this to display "Male" and "Female"(insted of "M" of "F") while performing GET request. </p>
  
  <p>This works fine. </p>
  
  <p>But now I am writing an patch method for the model and <code>SerializerMethodField()</code> has <code>read_only=True</code>. So I am not getting value passed for gender field in <code>serializer.validated_data()</code>. How to overcome this issue?</p>