The Samurai Principle

[Lawrence D'Oliveiro]

In message <mailman.654.1284158340.29448.python-list at python.org>, Robert 
Kern wrote:

> On 9/10/10 5:17 PM, Lawrence D'Oliveiro wrote:
>
>> In message<mailman.567.1283927599.29448.python-list at python.org>, Ian
>> Kelly wrote:
>>
>>> And returning None on failure is dangerous, because if the programmer
>>> does not take care to handle that case, the program may attempt to
>>> regard it as actual data.
>>
>> But None *is* actual data.
> 
> And that is exactly the reason why the Samurai Principle says to not
> return None when the function fails to do what it intended to do.

How can the function “fail” when it returns what it is specified to return?