singletons.sentinel

Pythonic FP - Collection of singleton classes

final class pythonic_fp.singletons.sentinel.Sentinel(sentinel_name: str)

Singleton classes representing sentinel values.

• intended for library code, not to be exported/shared between modules

  • otherwise some of its intended typing guarantees may be lost

• useful substitute for None as a hidden sentinel value

  • allows None to be stored in data structures

  • allows end users to choose to use None or () as sentinel values

  • always equals itself (unlike NoValue)

Usage:

• import Sentinel and then either

  • define _my_sentinel: Final[Sentinel] = Sentinel('my_sentinel')

  • or use Sentinel('my_sentinel') directly

• compare using either

  • is and is not or == and !=

  • the Sentinel() value always equals itself

  • and never equals anything else, especially other sentinel values