[Tutor] Chutes & Ladders

[Peter Otten]

Keith Winston wrote:

> On Sun, Dec 22, 2013 at 3:04 PM, <tutor-request at python.org> wrote:
> 
>>
>> games = [p1.gameset(gamecount) for _ in range(multicount)]
> 
> 
> So Peter gave me a list of suggesttions, all of which I've incorporated
> and gotten running, and it's been instructive.
> 
> But in my haste I included the line above, cut & pasted from his
> suggestion, without understanding what the underscore is doing in there. I
> think I understand that at the prompt of the interpreter the underscore
> returns the last value returned... but I can't really figure out what it's
> doing here.

There is a convention (recognized by pylint) to have unused variables start 
with an underscore. The shortest of these names is just the underscore. I 
used it to indicate that the important thing is that gameset() is called, 
not whether it is the seventh or 42nd call. Following that convention a line 
counting script could look

linecount = 0
for _line in sys.stdin:
    linecount += 1
print(linecount, "lines")

while a script for adding line numbers would be

lineno = 1
for line in sys.stdin
    print("{:5}:".format(lineno), line, end="")
    lineno += 1

> Also: this statement worked fine:
> 
> for tmulti in games:
>     print("{moves:9.2f} {chutes:12.2f} {ladders:13.2f}".format(
>             moves=mean(tgset[1] for tgset in tmulti),
>             chutes=mean(tgset[2] for tgset in tmulti),
>             ladders=mean(tgset[3] for tgset in tmulti)
>             ))
> 
> Which is sort of awesome to me, but in my efforts to riff on it I've been
> stumped: if I want to further process the arrays/lists my list
> comprehensions are generating, I sort of can't, since they're gone: that
> is, if I wanted to use the entire len(tmulti) of them to determine grand
> total averages and variances, I can't. And if my array is large, I woudn't
> want to iterate over it over and over to do each of these steps, I think.
> Anyway, I'm just goofing on all this, for the learning value, but I'll
> appreciate any thoughts. Thanks.

You can modify the loop to

for tmulti in games:
    moves = [tgset[1] for tgset in tmulti]
    chutes = ...
    ladders = ...
    print("...".format(
        moves=mean(moves),
        chutes=mean(chutes),
        ladders=mean(ladders)
        ))

> I'm also trying to speed up the program at this point: the way I've set it
> up now it builds a list of lists (of lists) of all the stats of all the
> games of all the gamesets of all the multisets. I've visually  streamlined
> it some, without any effect on performance I can detect. Would using
> arrays, or tuples, or something else be likely to be faster? It's
> interesting that running it on my 8 y.o. Core 2 Duo and my 2 y.o. Core I5
> result in virtually exactly the same speed. Weird. Obviously, it's just
> doing simple math, pretty much

"Simple math" is where the overhead of CPython over languages like C is most 
significant.