merge json object at postgresql with plpythonu

gistfile1.sql

CREATE LANGUAGE PLPYTHONU;

CREATE OR REPLACE
FUNCTION merge_json(left JSON, right JSON)
  RETURNS JSON AS $$
  import simplejson as json
  def merge(source, destination):
    for key, value in source.items():
      if isinstance(value, dict):
        # get node or create one
        node = destination.setdefault(key, {})
        merge(value, node)
      else:
        destination[key] = value
    return destination
  l, r = json.loads(left), json.loads(right)
  l = merge(l, r)
  j = json.dumps(l)
  return j
$$ LANGUAGE PLPYTHONU;

UPDATE my_table SET my_field = merge_json(my_field::json, '{"foo":{"bar":true}}'::json);