What behavior would you expect?

[Dan Sommers]

On Fri, 20 Feb 2015 07:11:13 +1100, Chris Angelico wrote:

> On Fri, Feb 20, 2015 at 7:03 AM, Denis McMahon <denismfmcmahon at gmail.com> wrote:
>> On the one hand, the return type of a function (when it returns,
>> rather than raising an exception) should be consistent to itself,
>> even if using a language where types are not declared.
> 
> Yes, so I'd advise against having a function sometimes return a string
> and sometimes a dict. Sure. But None gets a bit of a special pass
> here; in a lot of languages, what you'd have is a "nullable" type (eg
> in C you might declare the return value as "pointer to char", and
> either return a pointer to a string, or NULL), but in Python, you
> return None for the special case. So in a sense, "str or None" is not
> so inconsistent.

I'm an old C and assembly language programmer, but the older I get, the
less I use null (in C or in Java), None (in Python), or equivalent in
other languages.  If a function can't perform its side effect (like
renaming a file), then raise an exception.  If a function called for its
value can't return that value, then raise an exception; if there are no
values to return, then return an empty collection.  How much code do we
write and read that checks for null (or None, or whatever), and how much
time do we spend writing it and reading it?

Readability counts.  Simple is better than complex.  Explicit is better
than implicit.  Errors should never pass silently.  In the face of
ambiguity, refuse the temptation to guess.  (Wow!  I knew I could turn
to the Zen for support, but I didn't realize just how much support I
would get!)

See also <http://en.wikipedia.org/wiki/Void_safety>.

Dan