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.
Sincerely
Thomas Philips
--
http://mail.python.org/mailman/listinfo/python-list
