Class _PlaceholderType

Lib/functools.py:273–293

The type of the Placeholder singleton. Used as a placeholder for partial arguments.

class _PlaceholderType:
    """The type of the Placeholder singleton.

    Used as a placeholder for partial arguments.
    """
    __instance = None
    __slots__ = ()

    def __init_subclass__(cls, *args, **kwargs):
        raise TypeError(f"type '{cls.__name__}' is not an acceptable base type")

    def __new__(cls):
        if cls.__instance is None:
            cls.__instance = object.__new__(cls)
        return cls.__instance

    def __repr__(self):
        return 'Placeholder'

    def __reduce__(self):
        return 'Placeholder'

Placeholder = _PlaceholderType()