[29869] in Perl-Users-Digest
Perl-Users Digest, Issue: 1112 Volume: 11
daemon@ATHENA.MIT.EDU (Perl-Users Digest)
Thu Dec 13 11:14:17 2007
Date: Thu, 13 Dec 2007 08:14:10 -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 Thu, 13 Dec 2007 Volume: 11 Number: 1112
Today's topics:
Re: split is not convinient <tadmc@seesig.invalid>
Re: split is not convinient <joost@zeekat.nl>
Re: split is not convinient <1usa@llenroc.ude.invalid>
Re: split is not convinient <ben@morrow.me.uk>
Re: split is not convinient <cwilbur@chromatico.net>
Re: Stupid Mistakes <inthepickle@gmail.com>
Re: Stupid Mistakes <ben@morrow.me.uk>
Re: Stupid Mistakes <josef.moellers@fujitsu-siemens.com>
Re: Stupid Mistakes <ben@morrow.me.uk>
Re: Stupid Mistakes <ben@morrow.me.uk>
Digest Administrivia (Last modified: 6 Apr 01) (Perl-Users-Digest Admin)
----------------------------------------------------------------------
Date: Thu, 13 Dec 2007 06:09:38 -0600
From: Tad J McClellan <tadmc@seesig.invalid>
Subject: Re: split is not convinient
Message-Id: <slrnfm2882.s8j.tadmc@tadmc30.sbcglobal.net>
Jürgen Exner <jurgenex@hotmail.com> wrote:
> Mark Seger wrote:
>> In fact I avoid any syntax that
>> has a default such as "while (<>)" which is why I always use "while
>> ($var=<>)".
I agree completely with this one.
Actually, it should most likely be:
while ( my $var = <> )
>> Are people that lazy that typing a few extra characters to
>> make what they're doing more explicit too much of a burden?
Many are. I am not one of them though. :-)
> I am somewhat torn. You certainly have a very valid point and taking
> shortcuts that lead to unreadable code is definitely not a good idea.
Understanding the code is not the big reason for avoiding while (<>).
Stomping on $_ without even local()izing it is the big reason IMO, it
can lead to classic "action at a distance".
>> How is
>> this any different from commenting code? Or don't people do that any
>> more either?
>
> Now that is actually comparing apples and oranges. I think you would agree
> that a comment like
> $index++ #increments $index by 1
> is nonsense.
It makes perfect sense.
> Correct, but still nonsense.
Correct, but without value
I could buy that one though. Or even
Correct, but with _negative_ value
(because now the code must be kept in sync with the comment)
> Comments should describe _what_ is
> being done,
I think you are misremembering the classic advice regarding comments.
The code already describes what is being done. Saying the same thing
twice does not add any value.
Comments should describe _why_ it is being done.
> not _how_ it is done. So the comment above should be something
> like "examine next personal file" or whatever action this increment
> indicates.
That comment is a "why" rather than a "what".
Q: Why is the programmer incrementing $index
A: To move on to processing the next personal file
--
Tad McClellan
email: perl -le "print scalar reverse qq/moc.noitatibaher\100cmdat/"
------------------------------
Date: 13 Dec 2007 14:24:27 GMT
From: Joost Diepenmaat <joost@zeekat.nl>
Subject: Re: split is not convinient
Message-Id: <4761409b$0$16792$e4fe514c@dreader27.news.xs4all.nl>
On Thu, 13 Dec 2007 06:09:38 -0600, Tad J McClellan wrote:
> Jürgen Exner <jurgenex@hotmail.com> wrote:
>> Mark Seger wrote:
>
>>> In fact I avoid any syntax that
>>> has a default such as "while (<>)" which is why I always use "while
>>> ($var=<>)".
>
>
> I agree completely with this one.
>
> Actually, it should most likely be:
>
> while ( my $var = <> )
>
As has been mentioned somewhere above, that's simply incorrect code in
most circumstances. while (<handle>) { ... } is a special case and if you
really must use a named variable the construct should be
while (defined(my $var = <>)) { ... }
Joost.
------------------------------
Date: Thu, 13 Dec 2007 15:13:29 GMT
From: "A. Sinan Unur" <1usa@llenroc.ude.invalid>
Subject: Re: split is not convinient
Message-Id: <Xns9A056803382C5asu1cornelledu@127.0.0.1>
Joost Diepenmaat <joost@zeekat.nl> wrote in
news:4761409b$0$16792$e4fe514c@dreader27.news.xs4all.nl:
> On Thu, 13 Dec 2007 06:09:38 -0600, Tad J McClellan wrote:
>
>> Jürgen Exner <jurgenex@hotmail.com> wrote:
>>> Mark Seger wrote:
>>
>>>> In fact I avoid any syntax that
>>>> has a default such as "while (<>)" which is why I always use "while
>>>> ($var=<>)".
>>
>>
>> I agree completely with this one.
>>
>> Actually, it should most likely be:
>>
>> while ( my $var = <> )
>>
>
> As has been mentioned somewhere above, that's simply incorrect code in
> most circumstances. while (<handle>) { ... } is a special case and if
> you really must use a named variable the construct should be
>
> while (defined(my $var = <>)) { ... }
As far as I know, the magic test for defined in a while loop is the same
whether you are reading into a $_ or any lexical variable. Here is a
short test:
C:\DOCUME~1\asu1\LOCALS~1\Temp\m> cat m.txt
0
1
2
3
4
C:\DOCUME~1\asu1\LOCALS~1\Temp\m> xxd m.txt
0000000: 300a 310a 0a32 0a33 0a0a 340a 0a 0.1..2.3..4..
C:\DOCUME~1\asu1\LOCALS~1\Temp\m> cat m.pl
#!/usr/bin/perl
use strict;
use warnings;
my $name = 'm.txt';
my %dispatch = (
without_defined => \&without_defined,
with_defined => \&with_defined,
without_var => \&without_var,
);
for my $case ( sort keys %dispatch ) {
print "$case:\n";
open my $f, '<', $name
or die "Cannot open '$name': $!";
$dispatch{ $case }->( $f );
close $f
or die "Cannot close '$name': $!";
}
sub without_defined {
my $f = shift;
while ( my $line = <$f> ) {
print decorate($line);
}
}
sub with_defined {
my $f = shift;
while ( defined( my $line = <$f> ) ) {
print decorate($line);
}
}
sub without_var {
my $f = shift;
while ( <$f> ) {
print decorate($_);
}
}
sub decorate {
my ($s) = @_;
$s =~ s/\n/</;
return "'$s'\n";
}
__END__
C:\DOCUME~1\asu1\LOCALS~1\Temp\m> m
Without var assignment in while:
'0<'
'1<'
'<'
'2<'
'3<'
'<'
'4<'
'<'
With 'defined' in while:
'0<'
'1<'
'<'
'2<'
'3<'
'<'
'4<'
'<'
Without 'defined' in while:
'0<'
'1<'
'<'
'2<'
'3<'
'<'
'4<'
'<'
--
A. Sinan Unur <1usa@llenroc.ude.invalid>
(remove .invalid and reverse each component for email address)
clpmisc guidelines: <URL:http://www.augustmail.com/~tadmc/clpmisc.shtml>
------------------------------
Date: Thu, 13 Dec 2007 15:18:51 +0000
From: Ben Morrow <ben@morrow.me.uk>
Subject: Re: split is not convinient
Message-Id: <r3v735-jpj2.ln1@osiris.mauzo.dyndns.org>
Quoth Joost Diepenmaat <joost@zeekat.nl>:
> As has been mentioned somewhere above, that's simply incorrect code in
> most circumstances. while (<handle>) { ... } is a special case and if you
> really must use a named variable the construct should be
>
> while (defined(my $var = <>)) { ... }
while (my $var = <HANDLE>) gets the same special-case treatment:
~% perl -MO=Deparse -e'while (my $x = <HANDLE>) { 1 }'
while (defined(my $x = <HANDLE>)) {
'???';
}
-e syntax OK
Ben
------------------------------
Date: 13 Dec 2007 10:41:33 -0500
From: Charlton Wilbur <cwilbur@chromatico.net>
Subject: Re: split is not convinient
Message-Id: <87d4ta61qq.fsf@mithril.chromatico.net>
>>>>> "JE" == Jürgen Exner <jurgenex@hotmail.com> writes:
JE> On the other hand a lot of the elegance of Perl comes from its
JE> default "work space". It is so ingrained in the Perl world
JE> that I would almost call it a prerequisit for programming in
JE> Perl. If you don't know how to take advantage of $_ and @_
JE> then maybe you shouldn't program in Perl or maintain Perl
JE> code.
I would add, here, that if you don't know when to *not* take advantage
of $_ and @_, you shouldn't program in Perl or maintain Perl code,
either -- and that knowing *when* and *whether* to use a feature of a
programming language is far more important than knowing *how* to use
that feature.
Charlton
--
Charlton Wilbur
cwilbur@chromatico.net
------------------------------
Date: Thu, 13 Dec 2007 05:47:21 -0800 (PST)
From: inthepickle <inthepickle@gmail.com>
Subject: Re: Stupid Mistakes
Message-Id: <39d1653b-d83b-4a94-ade0-aac8b60e0712@i12g2000prf.googlegroups.com>
Thanks for all of the input. I am no programmer and I am fairly new
to Perl. I got a lot of good suggestions here, and I will try to
incorporate them.
Thanks again.
------------------------------
Date: Thu, 13 Dec 2007 14:40:34 +0000
From: Ben Morrow <ben@morrow.me.uk>
Subject: Re: Stupid Mistakes
Message-Id: <2ss735-k5i2.ln1@osiris.mauzo.dyndns.org>
[please don't top-post]
Quoth Josef Moellers <josef.moellers@fujitsu-siemens.com>:
> Why so complicated? You don't need another call to findswfile(): just
> set $File::Find:prune = 1 at the place where you decide that you don't
> need to go further.
The OP was attempting the search in this order:
Y:/BASEDIR/SUBDIR
Y:/BASEDIR
Y:/
, the point being that Y:/BASEDIR/SUBDIR is searched *before* the rest
of Y:/BASEDIR (presumably s?he feels the file is more likely to be found
there). While this could be emulated with one find, with bydepth => 1
and preprocess set to a sub that sorted BASEDIR/SUBDIR and BASEDIR first
in their respective directories, three finds are probably just as clear,
especially given the OP's apparent inexperience with Perl. Searching
SUBDIR three times I would expect to have negligible effect, as the
directories will all be in the cache.
Ben
------------------------------
Date: Thu, 13 Dec 2007 16:03:26 +0100
From: Josef Moellers <josef.moellers@fujitsu-siemens.com>
Subject: Re: Stupid Mistakes
Message-Id: <fjrhk2$9ab$1@nntp.fujitsu-siemens.com>
Ben Morrow wrote:
> [please don't top-post]
I didn't top-post, I quoted your code and amended it ;-)
As for your reply: I don't quite understand how setting a global=20
variable and checking it immediately on the next entry to findswfile()=20
and aborting *then* is better than aborting immeiately the file is found?=
--=20
These are my personal views and not those of Fujitsu Siemens Computers!
Josef M=F6llers (Pinguinpfleger bei FSC)
If failure had no penalty success would not be a prize (T. Pratchett)
Company Details: http://www.fujitsu-siemens.com/imprint.html
------------------------------
Date: Thu, 13 Dec 2007 15:32:11 +0000
From: Ben Morrow <ben@morrow.me.uk>
Subject: Re: Stupid Mistakes
Message-Id: <rsv735-jpj2.ln1@osiris.mauzo.dyndns.org>
Quoth Josef Moellers <josef.moellers@fujitsu-siemens.com>:
> Ben Morrow wrote:
> > [please don't top-post]
>
> I didn't top-post, I quoted your code and amended it ;-)
Not my code. You were replying to 'A. Bax'.
> As for your reply: I don't quite understand how setting a global
> variable and checking it immediately on the next entry to findswfile()
> and aborting *then* is better than aborting immeiately the file is found?
Ah. I misunderstood you. Had your reply been properly below the piece of
code you were talking about, that wouldn't have happened. ;)
Ben
------------------------------
Date: Thu, 13 Dec 2007 15:37:48 +0000
From: Ben Morrow <ben@morrow.me.uk>
Subject: Re: Stupid Mistakes
Message-Id: <c70835-jpj2.ln1@osiris.mauzo.dyndns.org>
[please wrap articles at ~72 characters]
Quoth "A. Bax" <c7eqjyg02@sneakemail.com>:
> # matching of a literal full stop; collapse /\.sldprt/ || /
> \.SLDPRT/
> # into /\.sldprt/i .
These don't do the same thing. The latter matches '.SlDpRt'. This may or
may not be important to the OP.
> There is still a big performance hit
> because the
> # regexp /$swfile/ must be compiled for every call to
> findswfile(), but
> # fixing that requires more work.
No, there isn't. Perl keeps track of which variables were interpolated
into a regex, and only recompiles when they are changed. Thus, this will
only be recompiled once for each time through the outermost loop, as
desired.
> our $f = $File::Find::name; #directory and file
> name
Don't use our for simple file-scope variables. Use my at the top of the
file. our is for when you really need a package variable: generally,
when code outside this file needs access to it.
Ben
------------------------------
Date: 6 Apr 2001 21:33:47 GMT (Last modified)
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------------------------------
End of Perl-Users Digest V11 Issue 1112
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