Calculated RTL field handling in Django Rest Framework.

rtl_field.py

from unicodedata import bidirectional
from django.template.defaultfilters import striptags
from rest_framework import serializers

class RTLField(serializers.BooleanField):

    def __init__(self, *args, **kwargs):
        kwargs.setdefault("read_only", True)
        super(RTLField, self).__init__(*args, **kwargs)

    def to_native(self, value):
        value = striptags(value).replace(" ", "")[:100]
        score = sum([bidirectional(c) in ("R", "AL") for c in value])
        return bool(score and score >= (len(value) / 2))

#
#   Usage: 
#
#   class MySerializer(serializers.ModelSerializer):
#
#       class Meta:
#           model = MyModel
#           fields = ("id", "title", "content", "title_rtl", "content_rtl")
#
#       title_rtl = RTLField(source="title")
#       content_rtl = RTLField(source="content")
#