[Python-3000] Should len() clip to sys.maxsize or raise OverflowError?

[Guido van Rossum]

On Tue, Sep 2, 2008 at 11:14 AM, Daniel Stutzbach
<daniel at stutzbachenterprises.com> wrote:
> On Tue, Sep 2, 2008 at 12:26 PM, Guido van Rossum <guido at python.org> wrote:
>> I stand by my view. I might voice strong discomfort with raising an
>> exception because it doesn't fit in some implementation detail.
>
> Isn't that precisely what OverflowError is for?  ("it doesn't fit in some
> implementation detail")
>
> It seems to me that the Purity angle here would be to allow len() to return
> any Python int object.  The Practical angle wants to restrict it to
> sys.maxsize for performance reasons.  Throwing an OverflowError seems like a
> good way for Practical to cry, "Oops, I've been caught".
>
> (I'm interested in this issue because my list-like extension type can in
> some cases have a length greater than sys.maxsize)

The way I see it is that there are tons of ways I can think of how
raising OverflowError can break unsuspecting programs (e.g. code that
has been tested before but never with a humungous input), whereas
returning a "little white lie" would allow such code to proceed just
fine. Some examples of code that is inconvenienced by the exception:

if len(x): # used as non-empty test
if len(x) > 100: # used to guarantee we can access items 0 through 99
for i in range(len(x)): # will be broken out before reaching the end

-- 
--Guido van Rossum (home page: http://www.python.org/~guido/)