On May 13, 11:01 am, John Salerno <[EMAIL PROTECTED]> wrote:
> Ben Finney wrote:
> > I think that the idiom
>
> > for unused in xrange(10):
> > # do stuff with no reference to 'unused'
>
> > is quite common. Is that what you're asking about?
>
> Yes. I was more or less asking about the specific situation of using a
> for loop to do something X number of times, but I think the more
> generalized problem that everyone is talking about -- using a counter
> variable that is never referenced in the loop -- probably puts the point
> I was trying to make in a better light.
>
> The reason I even brought this up is because I remember someone saying a
> while back (probably here on the newsgroup) that the true use of a for
> loop was to iterate through a sequence (for the purpose of using that
> sequence), not to do something X number of times. Once they made this
> comment, I suddenly saw the for loop in a new (and I believe purer)
> light. That was the first time I realized what it was really meant
> to do.
>
> Using something like:
>
> for unused in xrange(10):
> # do stuff 10 times
>
> suddenly seemed to me like a hackish way to replace
>
> for (int i=0; i<10; i++) {
> // do stuff 10 times;
>
> }
>
> Not that I think the above code (C#) looks all that elegant either. But
> in C# there is a distinction between the above, and this:
>
> foreach (int i in sequence)
> // do something;
>
> which is more closely related to the Python for loop.
>
> Now, you could easily make the argument that the Python for loop is a
> much simpler tool to accomplish *both* of the above, and I suppose that
> makes sense. Seems a little silly to have two separate for loops to do
> these things. I just wasn't sure if the "counter" version of the Python
> for loop was considered slightly unpythonic.
What was unPythonic, I think, as most people would agree, is to use
for like this:
--
for i in xrange(len(lst)):
pass
--
In VB, my language before Python, I've never used For Each even for a
sequence (Array, in VB), it seems too messy back then. Now, with
Python that only allowed a foreach statement, I realized that I never
really needed a for i in range(10) at all. Most of the time the places
where I need to do that is where the code is just a test code that
loops a certain number of times (with randomized input data), almost
never (probably never) met that in a real program code. And even in
some of those cases, the variables are usually used too (as a test
argument to the function being tested) or for logging purpose.
On May 13, 8:25 pm, Larry Bates <[EMAIL PROTECTED]> wrote:
(snip)
> I use it quite often, especially if I want to implement a fixed number of
> retries on a communications channel.
>
> -Larry
That still have semantic meaning: 'tries'. If it was me, I'll go to
the trouble of giving names, since I would use it for logging or
informational purpose ('first try' 'second try' 'third try' 'no more
try').
I've never really met a real "do something n times" case, where the
variable doesn't hold any semantic meaning that I don't want to use
and is not a test case.
For me, a _ (or any other dummy variable[1]) is good enough and it's
easy to change if later I realized that I actually need to use the
variable. I agree though, that i, j, k for unused name is a bad choice
because single letter names is in common usage in mathematics.
[1] PEP 8 is useless if a certain code base has other agreed
convention, as long as the name used for a unused name in certain code
base is consistent (and probably documented), it never becomes a
problem.
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