core_serializers.py

class DynamicMethodField(serializers.Field):
    """Field that accepts instance methods and method kwargs."""

    def __init__(self, *args, **kwargs):
        """Extend DynamicMethodCharField.__init__.

        Args:
            method (str): Method on the instance to call.
            method_args (list): List of arguments to pass to the
                instance method.
            method_kwargs (dict): Dictionary of keyword arguments to
                pass to the instance method.

        Raises:
            Exception: If method is not passed.

        """
        self.method = kwargs.pop('method', None)
        if not self.method:
            raise Exception('Please provide a method to this serializer field.')
        self.method_args = kwargs.pop('method_args', [])
        self.method_kwargs = kwargs.pop('method_kwargs', {})

        super(DynamicMethodField, self).__init__(*args, **kwargs)

    def to_representation(self, obj):
        """Representation of instance method."""
        return getattr(obj, self.method)(*self.method_args, **self.method_kwargs)


class DynamicMethodCharField(DynamicMethodField, serializers.CharField):
    """CharField that accepts instance methods and method kwargs.

    Example:
        avatar_sm = DynamicMethodCharField(
            source='*', method='get_thumbnail',
            method_kwargs={'size': 'small'})

    """

    def __init__(self, *args, **kwargs):
        """Extend DynamicMethodCharField.__init__."""
        super(DynamicMethodCharField, self).__init__(*args, **kwargs)

serializers.py

from rest_framework import serializers

from core_serializers import DynamicMethodCharField

class SinglePhotoSerializer(serializers.Serializer):
    small = DynamicMethodCharField(
        source='*', required=False, method='get_thumbnail', method_kwargs={'size': 'small'},
        read_only=True)
    medium = DynamicMethodCharField(
        source='*', required=False, method='get_thumbnail', method_kwargs={'size': 'medium'},
        read_only=True)
    large = DynamicMethodCharField(
        source='*', required=False, method='get_thumbnail',
        method_kwargs={'size': 'large'}, read_only=True)

    class Meta:
        fields = ('small', 'medium', 'large',)

class PhotoSerializer(serializers.ModelSerializer):
    thumbnails = SinglePhotoSerializer(source='*', required=False, read_only=True)
  
    class Meta:
        model = Photo
        fields = ('thumbnails')