why is xrange able to go back to beginning in Python?
iterator, python, xrange
Solution
Because the `xrange` object produced by calling `xrange()` specifies an `__iter__` that provides a unique version of itself (actually, a separate `rangeiterator` object) each time it's iterated.
>>> x = xrange(3)
>>> type(x)
<type 'xrange'>
>>> i = x.__iter__()
>>> type(i)
<type 'rangeiterator'>
Problem
I've encountered this code from Most pythonic way of counting matching elements in something iterable ``` r = xrange(1, 10) print sum(1 for v in r if v % 2 == 0) # 4 print sum(1 for v in r if v % 3 == 0) # 3 ``` r is iterated once. and then it's iterated again. I thought if an iterator is once consumed then it's over and it should not be iterated again. Generator expressions can be iterated only once: ``` r = (7 * i for i in xrange(1, 10)) print sum(1 for v in r if v % 2 == 0) # 4 print sum(1 for v in r if v % 3 == 0) # 0 ``` enumerate(L) too: ``` r = enumerate(mylist) ``` and file object too: ``` f = open(myfilename, 'r') ``` Why does xrange behave differently?