[Python-Dev] PEP 0424: A method for exposing a length hint (original) (raw)

Steven D'Aprano steve at pearwood.info
Sun Jul 15 15:47:07 CEST 2012

Antoine Pitrou wrote:

The point is that 0 is a legitimate value for a length hint. Simple implementations of lengthhint will start returning 0 as a legitimate value and you will wrongly interpret that as "don't know", which kinds of defeat the purpose of length-hint ;)

That said, I don't think a special value for "is infinite" is useful. Just make -1 mean "I don't know".

You've obviously never accidentally called list on an infinite iterator wink

It's not the (eventual) MemoryError that is the problem. On some systems, this can cause the PC to become unresponsive as the OS tries to free an ever-increasing amount of memory. Been there, done that, on a production system. I had to do a hard reboot to fix it.

I think having a hint that says "there's no way this can succeed, fail immediately" is more useful than caring about the difference between a hint of 0 and a hint of 1.

-- Steven

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