Class directional_link

traitlets/traitlets.py:362–426

Link the trait of a source object with traits of target objects. Parameters ---------- source : (object, attribute name) pair target : (object, attribute name) pair transform: callable (optional) Data transformation between source and target. Examples --------

class directional_link:
    """Link the trait of a source object with traits of target objects.

    Parameters
    ----------
    source : (object, attribute name) pair
    target : (object, attribute name) pair
    transform: callable (optional)
        Data transformation between source and target.

    Examples
    --------
    >>> class X(HasTraits):
    ...     value = Int()

    >>> src = X(value=1)
    >>> tgt = X(value=42)
    >>> c = directional_link((src, "value"), (tgt, "value"))

    Setting source updates target objects:
    >>> src.value = 5
    >>> tgt.value
    5

    Setting target does not update source object:
    >>> tgt.value = 6
    >>> src.value
    5

    """

    updating = False

    def __init__(self, source: t.Any, target: t.Any, transform: t.Any = None) -> None:
        self._transform = transform if transform else lambda x: x
        _validate_link(source, target)
        self.source, self.target = source, target
        self.link()

    def link(self) -> None:
        try:
            setattr(
                self.target[0],
                self.target[1],
                self._transform(getattr(self.source[0], self.source[1])),
            )
        finally:
            self.source[0].observe(self._update, names=self.source[1])

    @contextlib.contextmanager
    def _busy_updating(self) -> t.Any:
        self.updating = True
        try:
            yield
        finally:
            self.updating = False

    def _update(self, change: t.Any) -> None: