[23769] in Perl-Users-Digest
Perl-Users Digest, Issue: 5973 Volume: 10
daemon@ATHENA.MIT.EDU (Perl-Users Digest)
Tue Dec 23 09:10:34 2003
Date: Tue, 23 Dec 2003 06:10:08 -0800 (PST)
From: Perl-Users Digest <Perl-Users-Request@ruby.OCE.ORST.EDU>
To: Perl-Users@ruby.OCE.ORST.EDU (Perl-Users Digest)
Perl-Users Digest Tue, 23 Dec 2003 Volume: 10 Number: 5973
Today's topics:
Posting Guidelines for comp.lang.perl.misc ($Revision: tadmc@augustmail.com
Re: Q about a module containing more than one class <xxala_qumsiehxx@xxyahooxx.com>
Re: replacing two EOL chars by one (Anno Siegel)
Re: Return all points with x km of y (Anno Siegel)
Re: shared and \&Function references. <nobull@mail.com>
Re: Tie::DBI problem -> new record is created instead o <notpublic@restricted.com>
Why cant I break here in Perl Debugger? (Sara)
Re: Why cant I break here in Perl Debugger? (Anno Siegel)
Digest Administrivia (Last modified: 6 Apr 01) (Perl-Users-Digest Admin)
----------------------------------------------------------------------
Date: Tue, 23 Dec 2003 02:22:26 -0600
From: tadmc@augustmail.com
Subject: Posting Guidelines for comp.lang.perl.misc ($Revision: 1.4 $)
Message-Id: <1qudnasjvd3fZnqiRVn-uA@august.net>
Outline
Before posting to comp.lang.perl.misc
Must
- Check the Perl Frequently Asked Questions (FAQ)
- Check the other standard Perl docs (*.pod)
Really Really Should
- Lurk for a while before posting
- Search a Usenet archive
If You Like
- Check Other Resources
Posting to comp.lang.perl.misc
Is there a better place to ask your question?
- Question should be about Perl, not about the application area
How to participate (post) in the clpmisc community
- Carefully choose the contents of your Subject header
- Use an effective followup style
- Speak Perl rather than English, when possible
- Ask perl to help you
- Do not re-type Perl code
- Provide enough information
- Do not provide too much information
- Do not post binaries, HTML, or MIME
Social faux pas to avoid
- Asking a Frequently Asked Question
- Asking a question easily answered by a cursory doc search
- Asking for emailed answers
- Beware of saying "doesn't work"
- Sending a "stealth" Cc copy
Be extra cautious when you get upset
- Count to ten before composing a followup when you are upset
- Count to ten after composing and before posting when you are upset
-----------------------------------------------------------------
Posting Guidelines for comp.lang.perl.misc ($Revision: 1.4 $)
This newsgroup, commonly called clpmisc, is a technical newsgroup
intended to be used for discussion of Perl related issues (except job
postings), whether it be comments or questions.
As you would expect, clpmisc discussions are usually very technical in
nature and there are conventions for conduct in technical newsgroups
going somewhat beyond those in non-technical newsgroups.
This article describes things that you should, and should not, do to
increase your chances of getting an answer to your Perl question. It is
available in POD, HTML and plain text formats at:
http://mail.augustmail.com/~tadmc/clpmisc.shtml
For more information about netiquette in general, see the "Netiquette
Guidelines" at:
http://andrew2.andrew.cmu.edu/rfc/rfc1855.html
A note to newsgroup "regulars":
Do not use these guidelines as a "license to flame" or other
meanness. It is possible that a poster is unaware of things
discussed here. Give them the benefit of the doubt, and just
help them learn how to post, rather than assume
A note about technical terms used here:
In this document, we use words like "must" and "should" as
they're used in technical conversation (such as you will
encounter in this newsgroup). When we say that you *must* do
something, we mean that if you don't do that something, then
it's unlikely that you will benefit much from this group.
We're not bossing you around; we're making the point without
lots of words.
Do *NOT* send email to the maintainer of these guidelines. It will be
discarded unread. The guidelines belong to the newsgroup so all
discussion should appear in the newsgroup. I am just the secretary that
writes down the consensus of the group.
Before posting to comp.lang.perl.misc
Must
This section describes things that you *must* do before posting to
clpmisc, in order to maximize your chances of getting meaningful replies
to your inquiry and to avoid getting flamed for being lazy and trying to
have others do your work.
The perl distribution includes documentation that is copied to your hard
drive when you install perl. Also installed is a program for looking
things up in that (and other) documentation named 'perldoc'.
You should either find out where the docs got installed on your system,
or use perldoc to find them for you. Type "perldoc perldoc" to learn how
to use perldoc itself. Type "perldoc perl" to start reading Perl's
standard documentation.
Check the Perl Frequently Asked Questions (FAQ)
Checking the FAQ before posting is required in Big 8 newsgroups in
general, there is nothing clpmisc-specific about this requirement.
You are expected to do this in nearly all newsgroups.
You can use the "-q" switch with perldoc to do a word search of the
questions in the Perl FAQs.
Check the other standard Perl docs (*.pod)
The perl distribution comes with much more documentation than is
available for most other newsgroups, so in clpmisc you should also
see if you can find an answer in the other (non-FAQ) standard docs
before posting.
It is *not* required, or even expected, that you actually *read* all of
Perl's standard docs, only that you spend a few minutes searching them
before posting.
Try doing a word-search in the standard docs for some words/phrases
taken from your problem statement or from your very carefully worded
"Subject:" header.
Really Really Should
This section describes things that you *really should* do before posting
to clpmisc.
Lurk for a while before posting
This is very important and expected in all newsgroups. Lurking means
to monitor a newsgroup for a period to become familiar with local
customs. Each newsgroup has specific customs and rituals. Knowing
these before you participate will help avoid embarrassing social
situations. Consider yourself to be a foreigner at first!
Search a Usenet archive
There are tens of thousands of Perl programmers. It is very likely
that your question has already been asked (and answered). See if you
can find where it has already been answered.
One such searchable archive is:
http://groups.google.com/advanced_group_search
If You Like
This section describes things that you *can* do before posting to
clpmisc.
Check Other Resources
You may want to check in books or on web sites to see if you can
find the answer to your question.
But you need to consider the source of such information: there are a
lot of very poor Perl books and web sites, and several good ones
too, of course.
Posting to comp.lang.perl.misc
There can be 200 messages in clpmisc in a single day. Nobody is going to
read every article. They must decide somehow which articles they are
going to read, and which they will skip.
Your post is in competition with 199 other posts. You need to "win"
before a person who can help you will even read your question.
These sections describe how you can help keep your article from being
one of the "skipped" ones.
Is there a better place to ask your question?
Question should be about Perl, not about the application area
It can be difficult to separate out where your problem really is,
but you should make a conscious effort to post to the most
applicable newsgroup. That is, after all, where you are the most
likely to find the people who know how to answer your question.
Being able to "partition" a problem is an essential skill for
effectively troubleshooting programming problems. If you don't get
that right, you end up looking for answers in the wrong places.
It should be understood that you may not know that the root of your
problem is not Perl-related (the two most frequent ones are CGI and
Operating System related), so off-topic postings will happen from
time to time. Be gracious when someone helps you find a better place
to ask your question by pointing you to a more applicable newsgroup.
How to participate (post) in the clpmisc community
Carefully choose the contents of your Subject header
You have 40 precious characters of Subject to win out and be one of
the posts that gets read. Don't waste them. Take care while
composing them, they are the key that opens the door to getting an
answer.
Spend them indicating what aspect of Perl others will find if they
should decide to read your article.
Do not spend them indicating "experience level" (guru, newbie...).
Do not spend them pleading (please read, urgent, help!...).
Do not spend them on non-Subjects (Perl question, one-word
Subject...)
For more information on choosing a Subject see "Choosing Good
Subject Lines":
http://www.cpan.org/authors/id/D/DM/DMR/subjects.post
Part of the beauty of newsgroup dynamics, is that you can contribute
to the community with your very first post! If your choice of
Subject leads a fellow Perler to find the thread you are starting,
then even asking a question helps us all.
Use an effective followup style
When composing a followup, quote only enough text to establish the
context for the comments that you will add. Always indicate who
wrote the quoted material. Never quote an entire article. Never
quote a .signature (unless that is what you are commenting on).
Intersperse your comments *following* each section of quoted text to
which they relate. Unappreciated followup styles are referred to as
"Jeopardy" (because the answer comes before the question), or
"TOFU".
Reversing the chronology of the dialog makes it much harder to
understand (some folks won't even read it if written in that style).
For more information on quoting style, see:
http://web.presby.edu/~nnqadmin/nnq/nquote.html
Speak Perl rather than English, when possible
Perl is much more precise than natural language. Saying it in Perl
instead will avoid misunderstanding your question or problem.
Do not say: I have variable with "foo\tbar" in it.
Instead say: I have $var = "foo\tbar", or I have $var = 'foo\tbar',
or I have $var = <DATA> (and show the data line).
Ask perl to help you
You can ask perl itself to help you find common programming mistakes
by doing two things: enable warnings (perldoc warnings) and enable
"strict"ures (perldoc strict).
You should not bother the hundreds/thousands of readers of the
newsgroup without first seeing if a machine can help you find your
problem. It is demeaning to be asked to do the work of a machine. It
will annoy the readers of your article.
You can look up any of the messages that perl might issue to find
out what the message means and how to resolve the potential mistake
(perldoc perldiag). If you would like perl to look them up for you,
you can put "use diagnostics;" near the top of your program.
Do not re-type Perl code
Use copy/paste or your editor's "import" function rather than
attempting to type in your code. If you make a typo you will get
followups about your typos instead of about the question you are
trying to get answered.
Provide enough information
If you do the things in this item, you will have an Extremely Good
chance of getting people to try and help you with your problem!
These features are a really big bonus toward your question winning
out over all of the other posts that you are competing with.
First make a short (less than 20-30 lines) and *complete* program
that illustrates the problem you are having. People should be able
to run your program by copy/pasting the code from your article. (You
will find that doing this step very often reveals your problem
directly. Leading to an answer much more quickly and reliably than
posting to Usenet.)
Describe *precisely* the input to your program. Also provide example
input data for your program. If you need to show file input, use the
__DATA__ token (perldata.pod) to provide the file contents inside of
your Perl program.
Show the output (including the verbatim text of any messages) of
your program.
Describe how you want the output to be different from what you are
getting.
If you have no idea at all of how to code up your situation, be sure
to at least describe the 2 things that you *do* know: input and
desired output.
Do not provide too much information
Do not just post your entire program for debugging. Most especially
do not post someone *else's* entire program.
Do not post binaries, HTML, or MIME
clpmisc is a text only newsgroup. If you have images or binaries
that explain your question, put them in a publically accessible
place (like a Web server) and provide a pointer to that location. If
you include code, cut and paste it directly in the message body.
Don't attach anything to the message. Don't post vcards or HTML.
Many people (and even some Usenet servers) will automatically filter
out such messages. Many people will not be able to easily read your
post. Plain text is something everyone can read.
Social faux pas to avoid
The first two below are symptoms of lots of FAQ asking here in clpmisc.
It happens so often that folks will assume that it is happening yet
again. If you have looked but not found, or found but didn't understand
the docs, say so in your article.
Asking a Frequently Asked Question
It should be understood that you may have missed the applicable FAQ
when you checked, which is not a big deal. But if the Frequently
Asked Question is worded similar to your question, folks will assume
that you did not look at all. Don't become indignant at pointers to
the FAQ, particularly if it solves your problem.
Asking a question easily answered by a cursory doc search
If folks think you have not even tried the obvious step of reading
the docs applicable to your problem, they are likely to become
annoyed.
If you are flamed for not checking when you *did* check, then just
shrug it off (and take the answer that you got).
Asking for emailed answers
Emailed answers benefit one person. Posted answers benefit the
entire community. If folks can take the time to answer your
question, then you can take the time to go get the answer in the
same place where you asked the question.
It is OK to ask for a *copy* of the answer to be emailed, but many
will ignore such requests anyway. If you munge your address, you
should never expect (or ask) to get email in response to a Usenet
post.
Ask the question here, get the answer here (maybe).
Beware of saying "doesn't work"
This is a "red flag" phrase. If you find yourself writing that,
pause and see if you can't describe what is not working without
saying "doesn't work". That is, describe how it is not what you
want.
Sending a "stealth" Cc copy
A "stealth Cc" is when you both email and post a reply without
indicating *in the body* that you are doing so.
Be extra cautious when you get upset
Count to ten before composing a followup when you are upset
This is recommended in all Usenet newsgroups. Here in clpmisc, most
flaming sub-threads are not about any feature of Perl at all! They
are most often for what was seen as a breach of netiquette. If you
have lurked for a bit, then you will know what is expected and won't
make such posts in the first place.
But if you get upset, wait a while before writing your followup. I
recommend waiting at least 30 minutes.
Count to ten after composing and before posting when you are upset
After you have written your followup, wait *another* 30 minutes
before committing yourself by posting it. You cannot take it back
once it has been said.
AUTHOR
Tad McClellan <tadmc@augustmail.com> and many others on the
comp.lang.perl.misc newsgroup.
------------------------------
Date: Wed, 17 Dec 2003 21:05:13 GMT
From: "Ala Qumsieh" <xxala_qumsiehxx@xxyahooxx.com>
Subject: Re: Q about a module containing more than one class
Message-Id: <cy3Eb.72340$o8.31793@newssvr25.news.prodigy.com>
"Ben Morrow" <usenet@morrow.me.uk> wrote in message
news:brqahf$jao$2@wisteria.csv.warwick.ac.uk...
>
> > I guess different people would do it differently. I would make is such
that
> > each module is in a separate file, and would name them such that each
'::'
> > in the module name corresponds to a real directory hierarchy. You don't
have
> > to do that of course, but I find it easier to look for files, and
understand
> > what class uses what. Something like this (untested):
>
> You seem to have missed the whole point of 'require'... anyone who
> keeps their Perl modules organised any differently from this is either
> a fool or knows something I don't.
No, I know exactly what require() and use() do. But, the OP had all the
classes in one file, in which case no require() is, well, required. Perhaps
my sentence wasn't completely clear. When I said "you don't have to do
that", I was referring to my previous sentence (all of it). If you decide
not to do that, then the OPs approach is fine, if you're so inclined.
And, in my example, I made sure I had a 'use ...' in the top most class.
--Ala
------------------------------
Date: 23 Dec 2003 12:04:21 GMT
From: anno4000@lublin.zrz.tu-berlin.de (Anno Siegel)
Subject: Re: replacing two EOL chars by one
Message-Id: <bs9b05$kd6$1@mamenchi.zrz.TU-Berlin.DE>
[newsgroups trimmed]
Sara <genericax@hotmail.com> wrote in comp.lang.perl.misc:
> tiltonj@erols.com (Jay Tilton) wrote in message
> news:<3fe4bd0e.68951468@news.erols.com>...
> > xah@xahlee.org (Xah Lee) wrote:
> >
> > : ... I want to replace two end of line characters by
> > : one end of line characters. The files in question is unix, and i'm
> > : also working under unix, so i did:
[snip complaint]
> > Preferrably one that is less petulant and profane than your article.
> > Frustration is no excuse for incivility.
>
> is incivility a word? Curious. Anyhow, if I understand this you want
> to replace two \n's with one? How about this (untested) code:
>
> die "Perl is ever so much smarter than Java\n" unless open F,
> 'myfile';
> my @f = <FILE>
> close F;
You just love reading entire files into memory.
> $f = join '',@f;
That could be had easier. Just undef $/ and read the file into $f
directly.
> $f =~ s/(\n)\n/$1/gs;
Uhg. This can be improved.
First off, /s modifies the behavior of "." in a regex and nothing else.
Since there is no "." in the regex, /s can go.
Then, since you know what you are matching, there is no need to
capture the match. Make that
$f =~ s/\n\n/\n/g;
However, this would keep two linefeeds from a sequence of three, and
roughly n/2 from each sequence of n. While this matches literally what
the OP wrote, I don't think that's what s/he intended.
$f =~ s/\n+/\n/g;
might come closer, but this is now better written as
$f =~ tr/\n//s;
For a more perlish solution, use "paragraph mode" (already mentioned
in this thread). It facilitates the treatment of line feeds, reading
each paragraph (block of text delimited by two or more linefeeds) and
normalizing the number of trailing line feeds to two. So this should
do it as well:
{
local $/ = ''; # paragraph mode
do { chomp; print "$_\n" } for <FILE>;
}
Anno
------------------------------
Date: 23 Dec 2003 11:24:14 GMT
From: anno4000@lublin.zrz.tu-berlin.de (Anno Siegel)
Subject: Re: Return all points with x km of y
Message-Id: <bs98ku$ivd$2@mamenchi.zrz.TU-Berlin.DE>
<ctcgag@hotmail.com> wrote in comp.lang.perl.misc:
> "Ian Pattison" <ianp@pop3.myrealbox.com> wrote:
> >
> > Thanks for all of your assistance on this one. Both for the programming
> > ideas as well as the geography/math lessons.
> >
> > My final result: I found a module on CPAN that would do all the
> > calculations I needed. (Geo-Distance-0.05) and from there it was simple.
> >
> > In response to Bob's question... I'm using Win32:ODBC to pull data from
> > an access database. Currently there are about 30 tables, each with around
> > 32,000 rows but in essence I'm using it as a flat file. I'm still working
> > exactly how to get the nearest, say, 500 to a given point but finding all
> > the ones with X km is done.
>
> I'd start by doing something like:
>
> my @data;
> while (my($key,$dist)=next_point()) {
> push @data, [$key,$dist];
> };
> @data = (sort {$a->[1]<=>$b->[1]})[0..$x-1];
Hmm... Sorting is not an efficient way to find the top n of a population
if n is considerably smaller than the population. Sorting is slow and
(usually) needs all the data in memory. Both can be avoided using a heap.
For this particular problem, we'd want a maximum heap, that is, one that
allows the extraction of the largest element at all times. Assuming we
have a Heap class with methods new, add, size and extract_maximum, this
finds the $x closest points:
my $heap = Heap->new( sub { $a->[1] <=> $b->[1] });
while ( my( $key, $dist) = next_point() ) {
$heap->add( [ $key, $dist]);
# discard the most distant point if no longer needed
$heap->extract_maximum if $heap->size > $x;
}
my @data = reverse map $heap->extract_maximum, 1 .. $heap->size;
If $x is small compared to the overall number n of locations, this runs
essentially in time proportional to n and space proportional to $x. If
$x approaches the total, it seamlessly mutates into a heap sort.
There are two or three heap modules on CPAN, though none of them may
have the interface I assumed.
> And if that took too much memory I'd do:
[snip]
The heap method does a better job of keeping intermediate storage small.
> And if that didn't cut I'd seriously look into getting a real
> GIS before I'd spend more time on rolling my own.
Indeed.
Anno
------------------------------
Date: 23 Dec 2003 12:40:56 +0000
From: Brian McCauley <nobull@mail.com>
Subject: Re: shared and \&Function references.
Message-Id: <u9ekuvu2p3.fsf@wcl-l.bham.ac.uk>
John William Aldis <John@nospam.syntagma.demon.co.uk> writes:
> In article <u9oeu1t30c.fsf@wcl-l.bham.ac.uk>, Brian McCauley
> <nobull@mail.com> writes
> >John William Aldis <John@nospam.syntagma.demon.co.uk> writes:
> >>I want to put a
> >> reference to a function into an item of one of these
> >I don't think you can have shared functions. (And, of course, you
> >can't put a reference to a non-shared thing in a shared variable).
>
> Thanks. I feared this would be the case.
>
> Does anyone know what the danger would be of letting people store
> \&Function references in their shared variables? AFAI can see, any
> thread that called that function would have it executed internally to
> said thread anyway.
package Wibble;
my $foo;
sub inc_foo {
$foo++;
}
&inc_foo contains references to %Wibble:: and $foo. Neither of those
are shared. &inc_foo therefore cannot be shared.
In principle an anonymous sub defined in the void package scope that
didn't enclose any unshared variables could be made sharable but I
suspect it would be a lot of effort for little gain.
--
\\ ( )
. _\\__[oo
.__/ \\ /\@
. l___\\
# ll l\\
###LL LL\\
------------------------------
Date: Tue, 23 Dec 2003 12:51:15 +0100
From: "Zoltan Kandi" <notpublic@restricted.com>
Subject: Re: Tie::DBI problem -> new record is created instead of updating existing one
Message-Id: <ifWFb.3$s04.10706@news.uswest.net>
> Dear Mr Zoltan:
>
> Hey loved you in that Tom Hanks movie.
What movie? I haven't been following Hollywood recently ;-)
> I don't understand why yuo're putting yourself through all of this
> with the ties. Those are OK for DBM or GDBM, but for a real database
> like mysql why not just use the usual mysel DBD driver, and fetch the
> rows you need? If this database gets sizable (which in my experience
> they ALL pretty much do eventually), tie-ing will be an unmanageable
> way to deal with it anyhow.
I've got about 10-12 small mysql database tables (up to 100 simple records
each) which are being changed every now and then by another script. The
script I wanted to use Tie::DBI with would once a minute update a GUI based
on the contents of these tables. Using Tie::DBI seemed to save some typing,
one would write:
foreach (sort keys %nodes) # my hash tied to the nodes MySQL table
{
$nodeimages{$_}->configure( -image =>
$myicons{$nodes{$_}->{NodeState}};
}
instead of
my $DBcmd = "SELECT NodeID,NodeState FROM nodes";
# 1 red
# 2 green
# 3 green
my $sth = $DBhandle->prepare($DBcmd);
$sth->execute();
while (my $ref = $sth->fetchrow_hashref())
{
$nodeimages[$ref->{NodeId}]->configure( -image =>
$myicons{$ref->{NodeState}};
}
$sth->finish();
One might say I was just lazy... but the example I gave should be working.
Merry Xmas,
Zoltan
------------------------------
Date: 23 Dec 2003 05:39:39 -0800
From: genericax@hotmail.com (Sara)
Subject: Why cant I break here in Perl Debugger?
Message-Id: <776e0325.0312230539.3bb361a7@posting.google.com>
I often want to break on the first line of a block, such as
21 while ($itsANiceDay)
22 {print "lets play outdoors\n";
23 $itsANiceDay = getWeatherReport();
24 }
I can set a breakpoint on like 21 or 23, but why not 22? It looks like
a legitimate place to break?
G
(sorry about posting this in the middle of another thread it was accidental.
------------------------------
Date: 23 Dec 2003 13:59:27 GMT
From: anno4000@lublin.zrz.tu-berlin.de (Anno Siegel)
Subject: Re: Why cant I break here in Perl Debugger?
Message-Id: <bs9hnv$kd6$3@mamenchi.zrz.TU-Berlin.DE>
Sara <genericax@hotmail.com> wrote in comp.lang.perl.misc:
> I often want to break on the first line of a block, such as
>
>
> 21 while ($itsANiceDay)
> 22 {print "lets play outdoors\n";
> 23 $itsANiceDay = getWeatherReport();
> 24 }
>
>
> I can set a breakpoint on like 21 or 23, but why not 22? It looks like
> a legitimate place to break?
>
> G
>
> (sorry about posting this in the middle of another thread it was accidental.
See my answer there.
Anno
------------------------------
Date: 6 Apr 2001 21:33:47 GMT (Last modified)
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Subject: Digest Administrivia (Last modified: 6 Apr 01)
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------------------------------
End of Perl-Users Digest V10 Issue 5973
***************************************
