On 5/2/2015 5:31 PM, Ian Kelly wrote:
Would it have been better if range() had been implemented as xrange()
from the beginning? Sure, that would have been great. Except for one
small detail: the iterator protocol didn't exist back then.
For loops originally used the getitem iterator protocol. xrange objects
have a __getitem__ method, but not __iter__ or __next__. As Mark
pointed out, they were introduced in 1993.
Getitem iterators still work. If iter(ob) is passed object ob without
.__iter__, iter looks for ob.__getitem__ and if present, returns
iterator(ob), where iterator is an internal protocol adapter class. Its
__next__ method calls ob.__getitem__ and converts IndexError to
StopIteration.
In 3.4.3:
class xrange:
def __init__(self, start, stop, step):
if step < 1:
raise ValueError('incomplete xrange require positive step')
self.val = start
self.stop = stop
self.step = step
def __getitem__(self, dummy):
val = self.val
self.val = val + self.step
if val < self.stop:
return val
else:
raise IndexError('')
it = iter(xrange(1, 10, 3))
print(type(it))
for i in it:
print(i)
#
<class 'iterator'>
1
4
7
--
Terry Jan Reedy
--
https://mail.python.org/mailman/listinfo/python-list
