[Python-Dev] PEP 418 is too divisive and confusing and should be postponed
zooko at zooko.com
Thu Apr 5 21:39:17 CEST 2012
Good job, Victor Stinner on baking the accumulated knowledge of this
thread into PEP 418. Even though I'm very interested in the topic, I
haven't been able to digest the whole thread(s) on the list and
understand what the current collective understanding is. The detailed
PEP document helps a lot.
I think there are still some mistakes, either in our collective
understanding as reflected by the PEP, or in my own head.
For starters, I still don't understand the first, most basic thing:
what do people mean when they say "monotonic clock"? I don't
understand the current text of PEP 418 with regard to the definition
of that word.
Allow me to resort to an analogy. There is an infinitely long,
perfectly straight and flat racetrack. There is a flag that gets
dragged along it at a constant rate, with the label "REAL TIME" on the
flag. There are some runners, each with a different label on their
Runner A: a helicopter hovers over Runner A. Occasionally it picks him
up and plops him down right next to the flag. Also, he wears a headset
and listens to instructions from his coach to run a little faster or
slower, as necessary, to remain abreast of the flag.
Runner B: a helicopter hovers over Runner B. If he is behind the flag,
it will pick him up and plop him down right next to the flag. However,
if he is ahead of the flag it will not pick him up.
Runner C: no helicopter ever picks up Runner C, but he does wear a
headset and listens to instructions from his coach to run a little
faster or a little slower. His coach tells him to run a little faster
if he is behind the flag or run a little slower if he is in front of
the flag, with the goal of eventually having him right next to the
Runner D: like Runner C, he never gets picked up, but he listens to
instructions to run a little faster or a little slower. However,
instead of telling him to run faster in order to catch up to the flag,
or to run slower in order to "catch down" to the flag, his coach
instead tells him to run a little faster if he is moving slower than
the flag is moving, and to run a little slower if he is moving faster
than the flag is moving. Note that this is very different from Runner
C, in that it is not intended to cause him to eventually be right next
to the flag, and indeed if it is done right it guarantees that he will
*never* be right next to the flag, although he will be moving just as
fast as the flag is moving.
Runner E: no helicopter, no headset. He just proceeds at his own pace,
blissfully unaware of the exhortations of others.
Now: which ones of these five runners do you call "monotonic"? Which
ones do you call "steady"?
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