[Python-Dev] Re: PEP 276 Simple Iterator for ints

[Skip Montanaro]

    >> * It would expose potentially significant optimizations that can't be
    >>   made today by eliminating the attribute lookup and function call to
    >>   range, and thus getting rid of that little bit of dynamism nobody
    >>   ever uses anyway.

    Tim> As I said last time this went around, I doubt the optimizations are
    Tim> significant: loop overhead is generally at worst a
    Tim> handful-of-percent thing in real programs, and the cost of one
    Tim> global lookup+call per entire loop (not per loop *trip*) isn't even
    Tim> measurable outside contrived examples.

I was thinking more along the lines of generating C or assembler on the
fly.  Knowing a priori the types of the values emitted by

    for i in [0, 1 .. 10]

are ints means that the code generator can mostly avoid dealing with "i" as
a Python int and instead use native ints.  In

    for i in range(11):

you'd have to examine the output of range() and for

    for i in xrange(11):

it might be "too difficult" (whatever that means) to ascertain the types of
the elements.

    ...

    Tim> (BTW, repeated addition is almost exactly the worst thing to do for
    Tim> fp sequences; doing starting_value + iteration_ordinal * step_value
    Tim> on each trip is usually much better behaved for floats.)

Yes, that's what I had in mind.

Skip