Custom callbacks

Callbacks run after the step pipeline and can inspect completed iterations, report progress, or control the run. They receive a StepContext; see Step context for its lifecycle and update methods. To perform work within the step pipeline, see Custom steps.

For ready-made plotting callbacks and their configuration, see Built-in callbacks.

Derive a callback from SMCCallback and implement apply. A callback receives the state produced by the current iteration, the current context, and the result accumulated so far:

from sequince.callbacks import SMCCallback


class ReportProgress(SMCCallback):
    def apply(self, state, context, result):
        print(f"iteration={context.t}, states={len(result)}")

An observational callback may return None. To update metadata or request a stop, return a replacement context:

class StopAfter(SMCCallback):
    def __init__(self, final_iteration):
        self.final_iteration = final_iteration

    def apply(self, state, context, result):
        if context.t >= self.final_iteration:
            return context.request_stop()
        return None

Callbacks run in their configured order. A replacement context returned by one callback is passed to the next callback and becomes result.context.