Class Tuple

traitlets/traitlets.py:3728–3854

An instance of a Python tuple.

class Tuple(Container[t.Tuple[t.Any, ...]]):
    """An instance of a Python tuple."""

    klass = tuple
    _cast_types = (list,)

    def __init__(self, *traits: t.Any, **kwargs: t.Any) -> None:
        """Create a tuple from a list, set, or tuple.

        Create a fixed-type tuple with Traits:

        ``t = Tuple(Int(), Str(), CStr())``

        would be length 3, with Int,Str,CStr for each element.

        If only one arg is given and it is not a Trait, it is taken as
        default_value:

        ``t = Tuple((1, 2, 3))``

        Otherwise, ``default_value`` *must* be specified by keyword.

        Parameters
        ----------
        *traits : TraitTypes [ optional ]
            the types for restricting the contents of the Tuple.  If unspecified,
            types are not checked. If specified, then each positional argument
            corresponds to an element of the tuple.  Tuples defined with traits
            are of fixed length.
        default_value : SequenceType [ optional ]
            The default value for the Tuple.  Must be list/tuple/set, and
            will be cast to a tuple. If ``traits`` are specified,
            ``default_value`` must conform to the shape and type they specify.
        **kwargs
            Other kwargs passed to `Container`
        """
        default_value = kwargs.pop("default_value", Undefined)
        # allow Tuple((values,)):
        if len(traits) == 1 and default_value is Undefined and not is_trait(traits[0]):
            default_value = traits[0]
            traits = ()

        if default_value is None and not kwargs.get("allow_none", False):
            # improve backward-compatibility for possible subclasses
            # specifying default_value=None as default,
            # keeping 'unspecified' behavior (i.e. empty container)
            warn(
                f"Specifying {self.__class__.__name__}(default_value=None)"
                " for no default is deprecated in traitlets 5.0.5."
                " Use default_value=Undefined",
                DeprecationWarning,
                stacklevel=2,
            )
            default_value = Undefined

        if default_value is Undefined:
            args: t.Any = ()
        elif default_value is None: