Re-save with MapReduce

#app.yaml mapreduce related
- url: /mapreduce/pipeline/images
  static_dir: mapreduce/lib/pipeline/ui/images

- url: /mapreduce.*
  script: mapreduce.main.APP
  login: admin


#mappers.py
from google.appengine.ext.mapreduce import operation as op
def resave(entity):
    yield op.db.Put(entity)


####mapreduce.yaml
mapreduce:
- name: My Mapreduce
  mapper:
    input_reader: google.appengine.ext.mapreduce.input_readers.DatastoreInputReader
    handler: mappers.resave
    params:
    - name: entity_kind
      default: models.MyModel