On Sat, Apr 11, 2015 at 02:15:49PM -0400, Joel Goldstick wrote: > On Sat, Apr 11, 2015 at 1:41 PM, Jim Mooney <cybervigila...@gmail.com> wrote: > > Why does the first range convert to a list, but not the second? > > > >>>> p = list(range(1,20)), (range(40,59)) > >>>> p > > ([1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19], > > range(40, 59)) > > > Assuming you are using python 3.x range is a generator, so it only > produces values if you iterate over it
Almost correct, but not quite. range, like xrange in Python 2, is not a generator, but a custom-made lazy sequence object. py> gen() # This actually is a generator. <generator object gen at 0xb7bd7914> py> range(1, 10) # This is not. range(1, 10) Range objects are special: not only do they produce values lazily as needed, but they also support len(), indexing, slicing, and membership testing, none of which generators are capable of doing: py> r = range(1, 30, 3) py> len(r) 10 py> r[8] # indexing 25 py> r[2:5] # slicing range(7, 16, 3) py> 9 in r # membership testing False py> 10 in r True All those results are calculated lazily, without having to pre-calculate a potentially enormous list. -- Steve _______________________________________________ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
