On Sun, 2 Oct 2016 12:28 am, Jussi Piitulainen wrote:
> I'm not sure any more to what message this should be a followup, but
> here is a demonstration of two different semantics of the for-loop
> variable scope/update, this time with nested loops using the same loop
> variable name. The first function, tabulate, uses Python semantics ("t"
> for true, if you like); the second, fabulate, is a translation ("f" for
> false, if you like) that uses the magical semantics where the loop
> variable is not only local to the loop but also a different variable on
> each iteration.
I'm sorry, I don't understand what you mean by "Python semantics" versus "a
translation". A translation of what? In what way is it "magical semantics"?
I see nothing magical in your code: it is Python code.
Of course, it is complex, complicated, convoluted, obfuscated, hard to
understand, non-idiomatic Python code, but there's nothing magical in it
(unless you count nonlocal as magic). And it does nothing that can't be
done more simply: just change the tabulate inner loop variable to a
different name.
def fabulate2(m, n):
# The simple, Pythonic, non-complicated way.
for i in range(m):
print(i, end = ': ')
c = 0
for j in range(n):
print(j, end = ', ' if j + 1 < n else ' : ')
c += 1
print(i, c)
Your version of tabulate and fabulate:
py> tabulate(3, 4)
0: 0, 1, 2, 3 : 3 4
1: 0, 1, 2, 3 : 3 4
2: 0, 1, 2, 3 : 3 4
py> fabulate(3, 4)
0: 0, 1, 2, 3 : 0 4
1: 0, 1, 2, 3 : 1 4
2: 0, 1, 2, 3 : 2 4
My simple version of fabulate:
py> fabulate2(3, 4)
0: 0, 1, 2, 3 : 0 4
1: 0, 1, 2, 3 : 1 4
2: 0, 1, 2, 3 : 2 4
> The latter property makes no difference in this
> demonstration, but the former does; there's also a spurious counter that
> is not local to the nested loops, just to be sure that it works as
> expected (it does).
>
> A summary of sorts: it's possible to demonstrate the scope difference in
> Python code, with no box in sight; boxes are irrelevant; the relevant
> issue is what function and when the loop variable is associated with,
> explicitly or implicitly.
I don't know what "scope difference" you think you are demonstrating.
tabulate() has a single scope, fabulate() has multiple scopes because it
has inner functions that take i as argument, making them local to the inner
functions. Um, yeah, of course they are different. They're different
because you've written them differently. What's your point?
As far as I can see, all you have demonstrated is that it is possible to
write obfuscated code in Python. But we already knew that.
--
Steve
“Cheer up,” they said, “things could be worse.” So I cheered up, and sure
enough, things got worse.
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