Tal Einat <taleinat+pyt...@gmail.com> added the comment:
... and they can be given excellent reprs by using a meta-class:
class Sentinel(type):
@classmethod
def __prepare__(cls, name, bases, **kwds):
d = super().__prepare__(name, bases, **kwds)
def __new__(cls_, *args, **kwargs):
raise TypeError(
f'{cls_!r} is a sentinel and cannot be instantiated')
d.update(__new__=__new__)
return d
def __repr__(cls):
return f'{cls.__module__}.{cls.__qualname__}'
class MISSING(metaclass=Sentinel): pass
This also has another nice benefit:
>>> type(MISSING)
<class 'sentinels.Sentinel'>
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Python tracker <rep...@bugs.python.org>
<https://bugs.python.org/issue44123>
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