import sys
if sys.version_info >= (3,):
xrange = range
def rev_range(*args):
"""Create a reversed range.
Equivalent to reversed(list(range(*args))), but without the intermediate
list.
This does some simple math on the arguments instead of creating an
intermediate list and reversing it, thus automating a simple but
error-prone optimization.
"""
# Before Python 3.0, range creates a list while xrange is an efficient
# iterator. From 3.0 onwards, range does what xrange did earlier (and
# xrange is gone).
if len(args) == 1:
# start = 0, stop = args[0], step = 1
return xrange(args[0]-1, -1, -1)
# Unpack arguments, setting 'step' to 1 if it is not given.
start, stop, step = (args + (1,))[:3]
# The new 'stop' is the first item of the original range plus/minus one,
# depending on the step's sign. Specifically:
# new_stop = start - (1 if step > 0 else -1)
#
# The new 'start' is the last item of the original range, which is
# between one and 'step' less than the original 'stop'. Specifically:
#
# * If 'stop' minus 'start' divides by 'step' then the last item of the
# original range is 'stop' minus 'step'.
# * If 'stop' minus 'start' doesn't divide by 'step', then the last item of
# the original range is 'stop' minus the remainder of this division.
#
# A single expression which accounts for both cases is:
# new_start = stop - ((stop-start-1) % step + 1)
return xrange(stop - ((stop-start-1) % step + 1),
start - (1 if step > 0 else -1),
-step)
Diff to Previous Revision
--- revision 15 2009-06-10 21:25:50
+++ revision 16 2014-03-29 12:43:26
@@ -1,22 +1,23 @@
+import sys
+if sys.version_info >= (3,):
+ xrange = range
+
def rev_range(*args):
"""Create a reversed range.
- Equivalent to reversed(list(range(*args))), but more efficient.
+ Equivalent to reversed(list(range(*args))), but without the intermediate
+ list.
This does some simple math on the arguments instead of creating an
intermediate list and reversing it, thus automating a simple but
- error-prone optimization often done by programmers.
+ error-prone optimization.
"""
# Before Python 3.0, range creates a list while xrange is an efficient
# iterator. From 3.0 onwards, range does what xrange did earlier (and
# xrange is gone).
- import sys
- if sys.version < "3":
- range = xrange
-
if len(args) == 1:
# start = 0, stop = args[0], step = 1
- return range(args[0]-1, -1, -1)
+ return xrange(args[0]-1, -1, -1)
# Unpack arguments, setting 'step' to 1 if it is not given.
start, stop, step = (args + (1,))[:3]
@@ -24,7 +25,7 @@
# The new 'stop' is the first item of the original range plus/minus one,
# depending on the step's sign. Specifically:
# new_stop = start - (1 if step > 0 else -1)
-
+ #
# The new 'start' is the last item of the original range, which is
# between one and 'step' less than the original 'stop'. Specifically:
#
@@ -35,6 +36,6 @@
#
# A single expression which accounts for both cases is:
# new_start = stop - ((stop-start-1) % step + 1)
- return range(stop - ((stop-start-1) % step + 1),
- start - (1 if step > 0 else -1),
- -step)
+ return xrange(stop - ((stop-start-1) % step + 1),
+ start - (1 if step > 0 else -1),
+ -step)
