In addition to the DB datastore exceptions, the NDB datastore provides the following exception classes:

exception ComputedPropertyError()
Raised when attempting to set a value to or delete a computed property.
exception InvalidPropertyError()
Raised when a property is not applicable to a given use. For example, a property must exist and be indexed to be used in a query's projection or group by clause.
exception ReadonlyPropertyError()
Raised when attempting to set a property value that is read-only.
exception UnprojectedPropertyError()
Raised when getting a property value that's not in the projection.
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App Engine standard environment for Python