The article never claims that anywhere. That makes it hard to interpret your comment because there are a few places where the article slightly conflates a non-

The article never claims that anywhere. That makes it hard to interpret your comment because there are a few places where the article slightly conflates a non-existent key with value == None and maybe you're obliquely referring to one of those, but I'm not sure which one. All of them are OK so long as the dictionary doesn't have having any values equal to None, which it should really spell out but is obviously implied. Actually, most of them even require that none of the values are falsey (e.g. 0, empty list, None, or indeed False). It would actually be possible to work around that but still fundamentally use the same ideas by using a sentinel value: # At file scope, not exposed _not_present_sentinel = object() # Version B def read(self, id_: str) -> Item: result = self.items.get(id_, _not_present_sentinel) if result is _not_present_sentinel: raise ItemNotFound(id_) return result