Function default

traitlets/traitlets.py:1200–1238

A decorator which assigns a dynamic default for a Trait on a HasTraits object. Parameters ---------- name The str name of the Trait on the object whose default should be generated. Notes ----- Unlike observers and validators which are properties of the HasTraits

(name: str)

def default(name: str) -> DefaultHandler:
    """A decorator which assigns a dynamic default for a Trait on a HasTraits object.

    Parameters
    ----------
    name
        The str name of the Trait on the object whose default should be generated.

    Notes
    -----
    Unlike observers and validators which are properties of the HasTraits
    instance, default value generators are class-level properties.

    Besides, default generators are only invoked if they are registered in
    subclasses of `this_type`.

    ::

        class A(HasTraits):
            bar = Int()

            @default('bar')
            def get_bar_default(self):
                return 11

        class B(A):
            bar = Float()  # This trait ignores the default generator defined in
                           # the base class A

        class C(B):

            @default('bar')
            def some_other_default(self):  # This default generator should not be
                return 3.0                 # ignored since it is defined in a
                                           # class derived from B.a.this_class.
    """
    if not isinstance(name, str):
        raise TypeError("Trait name must be a string or All, not %r" % name)
    return DefaultHandler(name)


FuncT = t.TypeVar("FuncT", bound=t.Callable[..., t.Any])