efficiency of range() and xrange() in for loops

[Fredrik Lundh]

Carl Banks wrote:

> > I wondered if the Python compiler could, as a special case, turn:
> >
> > for i in range(n)
> >
> > into compiled code equivalent to
> >
> > for i in itr
> >
> > where "itr" is a lightweight iterator that returns the same values as
> > iter(range(n)).
>
> Nope, out of the question for Python 2.x.  Note that the the builtin
> range could be rebound, or a global range could appear in the module,
> at run time.  There might even be a good reason to do so....  Point is,
> optimizing the call to range can break compatibility even in the for
> loop.

that could of course be addressed by turning for-in into a special method
on the range object...  map

    for variable in expression:
        block

to

    _value = expression
    try:
        _for = _value.__for__
    except AttributeError:
        _for = iter(_value).__for__
    _for(variable, block)

and tweak as necessary.

</F>