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Python 2 is no longer supported by the community. We recommend that you migrate Python 2 apps to Python 3.

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.

Note: There is no 1:1 mapping between RPCs and Futures. Multiple futures might be tied to a result from a single RPC.

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 iterable are done.

Arguments

futures: Iterable of Future objects.

Returns None.

wait_any(futures)

Wait until at least one of a iterable of Futures is done.

Arguments

futures: Iterable of Future objects.

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