[EMAIL PROTECTED] wrote:
> I need to create ranges that can start and end with real numbers.
> Searching this newsgroup brought me to a function that I then modified
> as follows:
>
> def myRange(iMin, iMax=None, iStep=1):
> """Extends range to real numbers. Wherever possible, use Python's
> range .
> In other cases, make the behavior follow the spirit of Python's
> range """
> epsilon = 1.e-8
>
> if iMax == None and iStep == 1:
> return range(int(iMin))
>
> elif type(iMin).__name__.lower() in ('int', 'long') and \
> type(iMax).__name__.lower() in ('int', 'long') and \
> type(iStep).__name__.lower() in ('int', 'long') and iStep !=
> 0:
> return range( iMin, iMax, iStep)
>
> elif iMin <= iMax and iStep > 0:
> return [ iMin+i*iStep for i in range( int(math.ceil((iMax -
> iMin - epsilon)/iStep)) )]
>
> elif iMin >= iMax and iStep < 0:
> return [ iMin+i*iStep for i in range(-int(math.ceil((iMin -
> iMax + epsilon)/iStep)) )]
>
> else:
> raise ValueError, 'Cannot construct a range with steps of size
> ' + str(iStep) + ' between ' + str(iMin) + ' and ' + str(iMax)
>
>
> The one part of my implementation that has me a bit queasy (i.e.
> works in my current application, but I can see it misbehaving
> elsewhere) is the addition/subtraction of a fixed epsilon to ensure
> that my rounding goes the right way. A clean implementation would
> modify epsilon based on the achievable level of precision given the
> particular values of iMax, iMin and iStep. I suspect this requires a
> detailed understanding of the implementation of floating point
> arithmetic, and would appreciate hearing any thoughts you might have
> on gilding this lily.
In addition to the comments of Stargaming, most of which I agree with, I
think you would be far better dropping the epsilon business and doing
something like:
# requires that minimum <= maximum; swap values if necessary
res = minimum
while res < maximum:
yield res
res += step
--
Michael Hoffman
--
http://mail.python.org/mailman/listinfo/python-list
