Much Ado About None: Sentinel Values in Python

3 comments

• lpghatguy 8 minutes ago
  When I was writing a bunch of Lua, I was a big fan of having a None sentinel value (Lua uses 'nil' for representing absence) and it was useful for a lot of things similar to Pydantic's MISSING.

  This distinction is something that I think is actually handy about JavaScript, and distinguishing between 'null' and 'undefined' is sometimes useful for similar reasons.
• RantyDave 24 minutes ago
  "A simple cache returns None both for a missing key and for a key that maps to None."

  No, it returns KeyError. Or at least it should.

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  • lyorig 13 minutes ago
    Perhaps the author has had their fair share of run-ins with libraries that didn't think their API through like that. But yes, they should.
• chowells 33 minutes ago
  I like it. I can't see how to do better while remaining compatible with Python idioms.