Class Callback

dask/callbacks.py:10–83

Base class for using the callback mechanism Create a callback with functions of the following signatures: >>> def start(dsk): ... pass >>> def start_state(dsk, state): ... pass >>> def pretask(key, dsk, state): ... pass >>> def posttask(key, result, dsk,

class Callback:
    """Base class for using the callback mechanism

    Create a callback with functions of the following signatures:

    >>> def start(dsk):
    ...     pass
    >>> def start_state(dsk, state):
    ...     pass
    >>> def pretask(key, dsk, state):
    ...     pass
    >>> def posttask(key, result, dsk, state, worker_id):
    ...     pass
    >>> def finish(dsk, state, failed):
    ...     pass

    You may then construct a callback object with any number of them

    >>> cb = Callback(pretask=pretask, finish=finish)

    And use it either as a context manager over a compute/get call

    >>> with cb:            # doctest: +SKIP
    ...     x.compute()

    Or globally with the ``register`` method

    >>> cb.register()
    >>> cb.unregister()

    Alternatively subclass the ``Callback`` class with your own methods.

    >>> class PrintKeys(Callback):
    ...     def _pretask(self, key, dask, state):
    ...         print("Computing: {0}!".format(repr(key)))

    >>> with PrintKeys():   # doctest: +SKIP
    ...     x.compute()
    """

    active: ClassVar[set[tuple[Callable | None, ...]]] = set()

    def __init__(
        self, start=None, start_state=None, pretask=None, posttask=None, finish=None
    ):
        if start:
            self._start = start
        if start_state:
            self._start_state = start_state
        if pretask:
            self._pretask = pretask
        if posttask:
            self._posttask = posttask
        if finish:
            self._finish = finish

    @property
    def _callback(self) -> tuple[Callable | None, ...]: