On Friday, May 8, 2015 at 10:04:02 AM UTC+5:30, Chris Angelico wrote:
> On Fri, May 8, 2015 at 2:06 PM, Rustom Mody wrote:
> >> > If the classic Pascal (or Fortran or Basic) sibling balanced abstractions
> >> > of function-for-value procedure-for-effect were more in the collective
> >> > consciousness rather than C's travesty of function, things might not have
> >> > been so messy.
> >>
> >> I'm not really sure that having distinct procedures, as opposed to
> >> functions
> >> that you just ignore their return result, makes *such* a big difference.
> >> Can
> >> you explain what is the difference between these?
> >>
> >> sort(stuff) # A procedure.
> >> sort(stuff) # ignore the function return result
> >>
> >> And why the first is so much better than the second?
> >
> > Here are 3 None-returning functions/methods in python.
> > ie semantically the returns are identical. Are they conceptually identical?
> >
> >>>> x=print(1)
> > 1
> >>>> x
> >>>> ["hello",None].__getitem__(1)
> >>>> {"a":1, "b":2}.get("c")
> >>>>
>
> Your second example is a poor one, as it involves calling a dunder
> method. But all you've proven with that is that the empty return value
> of Python is a real value, and can thus be stored and retrieved.
>
> With print(), you have a conceptual procedure - it invariably returns
> None, so it'll normally be called in contexts that don't care about
> the return value. What about sys.stdout.write(), though? That's most
> often going to be called procedurally - you just write your piece and
> move on - but it has a meaningful return value. In normal usage, both
> are procedures. The ability to upgrade a function from "always returns
> None" to "returns some occasionally-useful information" is one of the
> strengths of a unified function/procedure system.
>
> With .get(), it's actually nothing to do with procedures vs functions,
That's backwards.
get is very much a function and the None return is semantically significant.
print is just round peg -- what you call conceptual function -- stuffed into
square hole -- function the only available syntax-category
> but more to do with Python's use of None where C would most likely use
> NULL. By default, .get() uses None as its default return value, so
> something that isn't there will be treated as None. In the same way as
> your second example, that's just a result of None being a real value
> that you can pass around - nothing more special than that.
>
> The other thing you're seeing here is that the *interactive
> interpreter* treats None specially.
Yeah I know
And if python did not try to be so clever, I'd save some time with
student-surprises
> In a program, an expression
> statement simply discards its result, whether it's None or 42 or
> [1,2,3] or anything else. You could write an interactive interpreter
> that has some magic that recognizes that certain functions always
> return None (maybe by checking their annotations), and omits printing
> their return values, while still printing the return values of other
> functions.
Hoo Boy! You seem to be in the 'the-more-the-better' (of magic) camp
> I'm not sure what it'd gain you, but it wouldn't change the
> concepts or semantics surrounding None returns.
It would sure help teachers who get paid by the hour and would rather spend
time on technical irrelevantia than grapple with significant concepts
--
https://mail.python.org/mailman/listinfo/python-list
