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# Prospective Search Exceptions (Python)

#### Experimental!

Prospective Search is an experimental, innovative, and rapidly changing new feature for App Engine. Unfortunately, being on the bleeding edge means that we may make backwards-incompatible changes to Prospective Search. We will inform the community when this feature is no longer experimental.

The `google.appengine.api.prospective_search` package provides the following exception classes derived from the base `prospective_search.Error`:

exception QuerySyntaxError()
  Query syntax is invalid or refers to a field that does not exist in the document schema. See Query Language Overview.
exception apiproxy_errors.Error
  The function call failed. This may occur if there is an internal error. This exception is unlikely to be due to a problem with the application.
exception SubscriptionDoesNotExist()
  Subscription does not exist. Use list_subscriptions() to see all currently registered subscriptions.