Right now, if you create an entity like:

e = datastore.entity.Entity(key, ('data'))

The unindexable properties will be 'd', 'a', or 't'. Obviously in this case the user meant to specify:

e = datastore.entity.Entity(key, ('data',))

Perhaps the Entity constructor should verify that exclude_from_indexes is a list or tuple.

Here is the discussion where the user ran into this: https://groups.google.com/forum/#!topic/gcd-discuss/rqwF8CRdTAY