Nice explanation. Thank you very much.
Thanks, Arup Rakshit a...@zeit.io > On 15-Mar-2019, at 6:24 PM, Calvin Spealman <cspea...@redhat.com> wrote: > > This is actually part of a not entirely uncommon misconception that can arise > by comparing objects only by their > repr() outputs (the string representation created when you pass them to > print). > > You're comparing the ID or memory address of the objects and determining they > must be the same object. In this case, > it is a kind of illusion. The function is being garbage collected at the end > of each call to sort_by_last_letter() and then, on > the next call, that address is reused. It is just common for Python to take > the next available location, and that happens to > be the same because you're re-running generally the same code, so the same > number of objects are created and destroyed > each time. > > You can see this by making a slight change: try keeping references to ALL the > created functions and you'll see they all > have different IDs so long as none of them get cleaned up. Try this slightly > modified version: > > functions = [] > def sort_by_last_letter(strings): > def last_letter(s): > return s[-1] > print(last_letter) > functions.append(last_letter) > return sorted(strings, key=last_letter) > > Which produces this output: > > >>> sort_by_last_letter(['ghi', 'def', 'abc']) > <function sort_by_last_letter.<locals>.last_letter at 0x7f276dd571e0> > ['abc', 'def', 'ghi'] > >>> sort_by_last_letter(['ghi', 'def', 'abc']) > <function sort_by_last_letter.<locals>.last_letter at 0x7f276dd57268> > ['abc', 'def', 'ghi'] > >>> sort_by_last_letter(['ghi', 'def', 'abc']) > <function sort_by_last_letter.<locals>.last_letter at 0x7f276dd572f0> > ['abc', 'def', 'ghi'] > > On Fri, Mar 15, 2019 at 8:47 AM Arup Rakshit <a...@zeit.io > <mailto:a...@zeit.io>> wrote: > Hi, > > I am reading a book where it says that: > > Just like module-level function definitions, the definition of a local > function happens at run time when the def keyword is executed. Interestingly, > this means that each call to sort_by_last_letter results in a new definition > of the function last_letter. That is, just like any other name bound in a > function body, last_letter is bound separately to a new function each time > sort_by_last_letter is called. > > If that above is true, why the below program shows the same object reference > for last_letter every time I call function sort_by_last_letter. > > # file name is sample.py > > def sort_by_last_letter(strings): > def last_letter(s): > return s[-1] > print(last_letter) > return sorted(strings, key=last_letter) > > python3 -i sample.py > >>> sort_by_last_letter(['ghi', 'def', 'abc']) > <function sort_by_last_letter.<locals>.last_letter at 0x1051e0730> > ['abc', 'def', 'ghi'] > >>> sort_by_last_letter(['ghi', 'def', 'abc']) > <function sort_by_last_letter.<locals>.last_letter at 0x1051e0730> > ['abc', 'def', 'ghi'] > >>> sort_by_last_letter(['ghi', 'def', 'abckl']) > <function sort_by_last_letter.<locals>.last_letter at 0x1051e0730> > ['def', 'ghi', 'abckl'] > >>> > > > Thanks, > > Arup Rakshit > a...@zeit.io <mailto:a...@zeit.io> > > > > -- > https://mail.python.org/mailman/listinfo/python-list > <https://mail.python.org/mailman/listinfo/python-list> > > > -- > CALVIN SPEALMAN > SENIOR QUALITY ENGINEER > cspea...@redhat.com <mailto:cspea...@redhat.com> M: +1.336.210.5107 > <tel:+1.336.210.5107> <https://red.ht/sig> > TRIED. TESTED. TRUSTED. <https://redhat.com/trusted> -- https://mail.python.org/mailman/listinfo/python-list
