Occasionally in Python (and in programming in general), you’ll need an object which can be uniquely identified. Sometimes this unique object represents a stop value or a skip value and sometimes it’s an initial value. But in each of these cases you want your object to stand out from the other objects you’re working with.

When you need a unique value (a sentinel value maybe) None is often the value to reach for. But sometimes None isn’t enough: sometimes None is ambiguous.

In this a…