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Python

NDB Future Class

A Future represents the result of an asynchronous operation. When created, it probably doesn't have any result data. When the operation finishes, the Future gets the result. An application can call a Future object's get_result() method; if the result has arrived, the method returns it; otherwise, it waits for the result to arrive and then returns it.

  1. Instance Methods
  2. Class Methods

Instance Methods

check_success()
Check to see if the operation succeeded. Waits if necessary. Raises an exception if there was a problem; returns None if there was no problem.
done()
Returns True if the result (or exception) has arrived; otherwise, returns False. This function does not wait.
get_exception()
Waits if necessary; then returns the exception (or None if there was no exception). Returns the exception, doesn't raise it.
get_result()
Waits if necessary; then returns the result or raises the exception.
get_traceback()
Waits if necessary; then returns the exception's traceback object (or None if there was no traceback object). Python's traceback module has functions to print and work with traceback objects.
wait()
Waits until a result or exception arrives. Always returns None.

Class Methods

wait_all(futures)
Wait until all Futures in the passed list are done.

Arguments

futures
List of Future objects.

Returns None.

wait_any(futures)
Wait until at least one of a list of Futures is done.

Arguments

futures
List of Future objects.

Returns one Future that is done. (Returns None if the futures list is empty.)