[jfischer]

In this particular situation, there was no else. I probably added an else clause with an assert return_value == False, as the function call was a virtual dispatch that could have many implementations. Of course, I wouldn't do that for every if/then/else statement in my code. In general, I'd prefer a stricter language that only permitted a boolean as a condition in the IF statement, avoiding this problem altogether.

If you are using truthy/falsey values, I think it can be a code smell that you are not doing enough to catch invalid values up front or should normalize the values closer to their creation point.