Events

class ignite.engine.events.Events(value)

Events that are fired by the Engine during execution. Built-in events:

• STARTED : triggered when engine’s run is started

• EPOCH_STARTED : triggered when the epoch is started

• GET_BATCH_STARTED : triggered before next batch is fetched

• GET_BATCH_COMPLETED : triggered after the batch is fetched

• ITERATION_STARTED : triggered when an iteration is started

• ITERATION_COMPLETED : triggered when the iteration is ended

• DATALOADER_STOP_ITERATION : engine’s specific event triggered when dataloader has no more data to provide

• EXCEPTION_RAISED : triggered when an exception is encountered

• TERMINATE_SINGLE_EPOCH : triggered when the run is about to end the current epoch, after receiving a terminate_epoch() or terminate() call.

• EPOCH_COMPLETED : triggered when the epoch is ended. This is triggered even when terminate_epoch() is called, unless the flag skip_epoch_completed is set to True.

• TERMINATE : triggered when the run is about to end completely, after receiving terminate() call.

• COMPLETED : triggered when engine’s run is completed or terminated with terminate(), unless the flag skip_completed is set to True.

The table below illustrates which events are triggered when various termination methods are called.

Method	TERMINATE_SINGLE_EPOCH	EPOCH_COMPLETED	TERMINATE	COMPLETED
no termination	✗	✔	✗	✔
terminate_epoch()	✔	✔	✗	✔
terminate_epoch() with skip_epoch_completed=True	✔	✗	✗	✔
terminate()	✗	✔	✔	✔
terminate() with skip_completed=True	✗	✔	✔	✗

Since v0.3.0, Events become more flexible and allow to pass an event filter to the Engine:

engine = Engine()

# a) custom event filter
def custom_event_filter(engine, event):
    if event in [1, 2, 5, 10, 50, 100]:
        return True
    return False

@engine.on(Events.ITERATION_STARTED(event_filter=custom_event_filter))
def call_on_special_event(engine):
    # do something on 1, 2, 5, 10, 50, 100 iterations

# b) "every" event filter
@engine.on(Events.ITERATION_STARTED(every=10))
def call_every(engine):
    # do something every 10th iteration

# c) "once" event filter
@engine.on(Events.ITERATION_STARTED(once=50))
def call_once(engine):
    # do something on 50th iteration

# d) "before" and "after" event filter
@engine.on(Events.EPOCH_STARTED(before=30, after=10))
def call_before(engine):
    # do something in 11 to 29 epoch

# e) Mixing "every" and "before" / "after" event filters
@engine.on(Events.EPOCH_STARTED(every=5, before=25, after=8))
def call_every_itr_before_after(engine):
    # do something on 9, 14, 19, 24 epochs

Event filter function event_filter accepts as input engine and event and should return True/False. Argument event is the value of iteration or epoch, depending on which type of Events the function is passed.

Since v0.4.0, user can also combine events with |-operator:

events = Events.STARTED | Events.COMPLETED | Events.ITERATION_STARTED(every=3)
engine = ...

@engine.on(events)
def call_on_events(engine):
    # do something

Since v0.4.0, custom events defined by user should inherit from EventEnum :

class CustomEvents(EventEnum):
    FOO_EVENT = "foo_event"
    BAR_EVENT = "bar_event"

COMPLETED = 'completed'

triggered when engine’s run is completed, or after receiving terminate() call.

DATALOADER_STOP_ITERATION = 'dataloader_stop_iteration'

engine’s specific event triggered when dataloader has no more data to provide

EPOCH_COMPLETED = 'epoch_completed'

Event attribute indicating epoch is ended.

EPOCH_STARTED = 'epoch_started'

triggered when the epoch is started.

EXCEPTION_RAISED = 'exception_raised'

triggered when an exception is encountered.

GET_BATCH_COMPLETED = 'get_batch_completed'

triggered after the batch is fetched.

GET_BATCH_STARTED = 'get_batch_started'

triggered before next batch is fetched.

INTERRUPT = 'interrupt'

triggered when the run is interrupted, after receiving interrupt() call.

ITERATION_COMPLETED = 'iteration_completed'

triggered when the iteration is ended.

ITERATION_STARTED = 'iteration_started'

triggered when an iteration is started.

STARTED = 'started'

triggered when engine’s run is started.

TERMINATE = 'terminate'

triggered when the run is about to end completely, after receiving terminate() call.

TERMINATE_SINGLE_EPOCH = 'terminate_single_epoch'

triggered when the run is about to end the current epoch, after receiving a terminate_epoch() call.