On Sat, Feb 15, 2014 at 2:14 PM, Rustom Mody <rustompm...@gmail.com> wrote: > On Saturday, February 15, 2014 8:12:14 AM UTC+5:30, Chris Angelico wrote: >> Well, for a start, I'd use Python 3, so there's no need to explain why >> some numbers have an L after them :) > > Nice point! > And only sharpens what I am saying -- python 3 is probably more confusing than > 2 wrt object identity
How so? Py3 eliminates an unnecessary difference: >>> 1L == 1 True >>> 1L is 1 False In Py3, this can't happen, because there simply is no distinction. (That said, the Py3 unification does mean that small integers pay the performance cost of long integers. I've mentioned before that it may be worth having an "under the covers" optimization whereby small integers are stored in a machine word - but this should be utterly invisible to the user. As far as the programmer's concerned, an int is an int is an int.) >> When it's utterly impossible for it to matter in any way, Python is >> allowed to reuse objects. >> >> I think that's simple enough to explain. There's nothing you can do to >> distinguish one 6 from another, so Python's allowed to have them the >> same. > > Simple?? > >>>> x=1234 >>>> y=1234 >>>> x is y > False >>>> 1234 is 1234 > True >>>> x=123 >>>> y=123 >>>> x is y > True In all three cases, Python is allowed to use separate objects. Nothing forces them to be shared. But in all three cases, there's no way you could distinguish one from another, so Python's allowed to reuse the same object. > "utterly impossible to matter"... > "nothing you can do to distinguish one 6 from another" > > All depend on doing one of these 3 for dealing with object identity > 1. Circular definition > 2. Delve into implementation > 3. Wildly wave the hands How do you distinguish between any other identical things? Once you've decided that they're equal, somehow you need to separate identity from value. I could have three six-sided dice, all made from the same mould, and yet each one is a separate object. If I hold all three in my hand and toss them onto the table, can I recognize which one is which? No, they're identical. Are they distinct objects? Yes. ChrisA -- https://mail.python.org/mailman/listinfo/python-list
