xrange
function doesn't work for large integers:
>>> N = 10**100
>>> xrange(N)
Traceback (most recent call last):
...
OverflowError: long int too large to convert to int
>>> xrange(N, N+10)
Traceback (most recent call last):
...
OverflowError: long int too large to convert to int
Python 3.x:
>>> N = 10**100
>>> r = range(N)
>>> r = range(N, N+10)
>>> len(r)
10
Is there a backport of py3k builtin range()
function for Python 2.x?
I'm looking for a complete implementation of "lazy" range()
, not just a partial implementation of some of its functionality.
I believe there is no backport (Py 3's completely removed the int/long distinction, after all, but in 2.* it's here to stay;-) but it's not hard to hack your own, e.g....:
import operator
def wowrange(start, stop, step=1):
if step == 0:
raise ValueError('step must be != 0')
elif step < 0:
proceed = operator.gt
else:
proceed = operator.lt
while proceed(start, stop):
yield start
start += step
Edit it appears the OP doesn't just want looping (the normal purpose of xrange, and
range in Py3), but also len
and the in
operator (the latter does work on the above generator, but slowly -- optimizations are possible). For such richness a class
is better...:
import operator
class wowrange(object):
def __init__(self, start, stop=None, step=1):
if step == 0: raise ValueError('step must be != 0')
if stop is None: start, stop = 0, start
if step < 0:
self.proceed = operator.gt
self.l = (stop-start+step+1)//step
else:
self.proceed = operator.lt
self.l = (stop-start+step-1)//step
self.lo = min(start, stop)
self.start, self.stop, self.step = start, stop, step
def __iter__(self):
start = self.start
while self.proceed(start, self.stop):
yield start
start += self.step
def __len__(self):
return self.l
def __contains__(self, x):
if x == self.stop:
return False
if self.proceed(x, self.start):
return False
if self.proceed(self.stop, x):
return False
return (x-self.lo) % self.step == 0
I wouldn't be surprised if there's an off-by-one or similar glitch lurking here, but, I hope this helps!
Edit again: I see indexing is ALSO required. Is it just too hard to write your own __getitem__
? I guess it is, so here it, too, is, served on a silver plate...:
def __getitem__(self, i):
if i < 0:
i += self.l
if i < 0: raise IndexError
elif if i >= self.l:
raise IndexError
return self.start + i * self.step
I don't know if 3.0 range
supports slicing (xrange
in recent 2.*
releases doesn't -- it used to, but that was removed because the complication was ridiculous and prone to bugs), but I guess I do have to draw a line in the sand somewhere, so I'm not going to add it;-).