> makes the error message longer

Out of curiosity is there a guide as to what is considered a too long error message ?

Or is there a technical reason like after a certain length strings are not cached and exception will be slower to construct ? I'm trying to understand why rhettinger would have proposed in his talk to make this specific error message longer and there is a push back now. 

> and since "del" is rarely used for deleting local variables I afraid that it can add confusion in most cases.

> The "del" statement is not the only way to unset the local variable.

Good point, would "or has been unset" be acceptable ?