(redmist) Efficient Perl Programming
by redmist (Deacon) on Nov 08, 2000 at 23:35 UTC
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RE: Efficient Perl Programming
by KM (Priest) on Nov 08, 2000 at 22:54 UTC
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Re: Efficient Perl Programming
by little (Curate) on Nov 08, 2000 at 22:57 UTC
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I do personally like "Effective programming perl" (J.N.Hall, R.Schwartz, Addison-Wesley, look up effectiveperl.com for samples or Book Reviews for reviews by arturo and jbardhan) very much. On the other hand it's at least to me always interesting to read merlyn's columns (always tricky and full of magic) and to read nodes from the past, especially in the code section or trying to read and to get module sources, but that's still hard to me. :-)
Have a nice day
All decision is left to your taste | [reply] |
RE: Efficient Perl Programming
by arturo (Vicar) on Nov 08, 2000 at 22:48 UTC
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Chapter 8 of the second ed. Camel has a bunch of things (and on different kinds of efficiency).
Other n' that I don't know of a central repository. Perhaps an addition to the Tutorial page is in order ...
Philosophy can be made out of anything. Or less -- Jerry A. Fodor
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Re: Efficient Perl Programming
by tedv (Pilgrim) on Nov 08, 2000 at 22:51 UTC
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Yes, there are, but I mostly know of ones in print. The
O'Reilly Perl 5 book has a two good sections on efficiency
and coding style on pages 537-550. The O'Reilly Regular
expression book has a lot of information scattered in it
about what makes particular regular expressions fast or
slow. (In particular, do not use $`, $&,
or $'.)
Naturally, the entire Perl Cookbook is a resource on how to
do particular tasks efficiently, and makes a good starting
point. Lastly, there is this great site
about perl where you can search for all things perl related. If you
had a particular question, I'm sure you could find the answer there. :)
-Ted | [reply] [d/l] [select] |
(Aighearach) Re: Efficient Perl Programming
by Aighearach (Initiate) on Nov 10, 2000 at 18:14 UTC
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What I would advise if you want to get your program running faster, is to use Devel::OpProf. This ties right into the perlfaq 3 question, "How do I make my Perl program run faster?" The advice given is to improve your algorithm. Okay, but how to do that? One of the best ways to compare different ways of doing things is to look at the resources they take up. Benchmark.pm will tell you how fast a code fragment runs, but that information isn't very portable. On a machine with lots of RAM, you might be developing programs that are very fast, but will generally lag on other people's machines. Devel::OpProf lets you identify these bottlenecks, even when they aren't slowing you down.
As an example, lets consider that we want to make a list of 1000 elements, with each element set to 1.
#!/usr/bin/perl -w
use strict;
use Devel::OpProf qw( profile print_stats zero_stats );
use Benchmark qw( timethese );
profile(1);
print "*** one() ***\n";
my @one = one();
print_stats();
zero_stats();
print "\n*** two() ***\n";
my @two = two();
print_stats();
zero_stats();
print "\n*** three() ***\n";
my @three = three();
print_stats();
zero_stats();
print "\n*** four() ***\n";
my @four = four();
print_stats();
zero_stats();
timethese( 0, {
test_one => 'one()',
test_two => 'two()',
test_three => 'three()',
test_four => 'four()'
} );
sub one {
my @list;
for ( my $i = 0; $i < 1000; $i++ ) {
$list[$i] = 1;
}
return @list;
}
sub two {
my @list;
for ( 0..999 ) {
$list[$_] = 1;
}
return @list;
}
sub three {
my @list = map { 1 } (1..1000);
return @list;
}
sub four {
my @list;
@list[0..999] = (1) x 1000;
return @list;
}
On my machine, this outputs:
*** one() ***
private variable 3002
constant item 2003
next statement 1009
private array 1004
numeric lt (<) 1001
logical and (&&) 1001
scalar assignment 1001
preincrement (++) 1000
iteration finalizer 1000
array element 1000
pushmark 8
glob value 4
subroutine entry 3
conditional expression 1
list assignment 1
block entry 1
array dereference 1
loop entry 1
loop exit 1
return 1
print 1
*** two() ***
next statement 2009
private array 1004
constant item 1003
foreach loop iterator 1001
logical and (&&) 1001
array element 1000
scalar variable 1000
iteration finalizer 1000
scalar assignment 1000
pushmark 9
glob value 5
subroutine entry 3
block entry 1
list assignment 1
conditional expression 1
array dereference 1
foreach loop entry 1
loop exit 1
return 1
print 1
*** three() ***
null operation 1002
constant item 1002
map iterator 1000
block 1000
pushmark 11
next statement 8
private array 4
glob value 4
subroutine entry 3
array dereference 2
list assignment 2
map 1
block entry 1
conditional expression 1
return 1
print 1
*** four() ***
pushmark 12
next statement 9
private array 5
glob value 4
constant item 4
subroutine entry 3
array dereference 2
list assignment 2
repeat (x) 1
conditional expression 1
null operation 1
array slice 1
block entry 1
return 1
print 1
Benchmark: running test_four, test_one, test_three, test_two, each for at least 3 CPU seconds...
test_one: 3 wallclock secs ( 3.16 usr + 0.00 sys = 3.16 CPU) @ 274.68/s (n=868)
test_two: 3 wallclock secs ( 3.25 usr + 0.00 sys = 3.25 CPU) @ 359.08/s (n=1167)
test_three: 3 wallclock secs ( 3.01 usr + 0.00 sys = 3.01 CPU) @ 408.64/s (n=1230)
test_four: 3 wallclock secs ( 3.27 usr + 0.01 sys = 3.28 CPU) @ 501.83/s (n=1646)
So, while Benchmark could tell us which is faster, it doesn't really tell us why. Devel::OpProf shows us that it is because of the number of temporary variables, &&'s, assignments, etc.
(while not really relevant to the point of this post, I should point out that probably a better idea than the slice in #4 is to just my @list = (1) x 1000;, because it is more readable. But, you are welcome to profile them to see if there is an algorithmical difference... ;)
Paris Sinclair | 4a75737420416e6f74686572
pariss@efn.org | 205065726c204861636b6572
http://sinclairinternetwork.com
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I was a little more interested in finding documentation (perldoc-style if nothing else), or a niche waiting to be filled by some useful documentation, on general optimization tips (e.g. use !/\S/ instead of /^\s*$/ and why). This information might still be useful to others though. Thanks.
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$churchill = qq{"If I were your husband," he said, "I should drink
+ it."};
while ($churchill =~ /"(.*?)"/g) {
print $1, "\n";
}
The purpose of the (.*?) is to capture
a quoted part of the string in $churchill.
Beginners usually try (.*) which doesn't work, because
it captures everything from the first quotation mark to the last,
including the non-quoted part in between. So then they ask
how to fix this and are advised to use (.*?)
instead. This does work, but it's much slower than it needs to be.
A faster solution is:
while ($churchill =~ /"([^"]*)"/g) {
print $1, "\n";
}
This says that what you're interested in is a quote character, followed by a sequence of
characters that are not quotes ([^"]) followed
by another quote. The description of what you want is more exact,
and it enables Perl to do the matching more efficiently.
So a good rule of thumb is to avoid .*? wherever possible
and to use something like [^"]* instead when you can.
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Paris Sinclair | 4a75737420416e6f74686572
pariss@efn.org | 205065726c204861636b6572
http://sinclairinternetwork.com
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Re: Efficient Perl Programming
by japhy (Canon) on Nov 09, 2000 at 00:45 UTC
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I've been wanting to write a book of some sort, a compendium
of elegant Perl idioms. Were that this book existed, I would
point you to it. ;)
$_="goto+F.print+chop;\n=yhpaj";F1:eval | [reply] |
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I don't think that
"a compendium of elegant Perl idioms" will be a good description of
the Perl Advanced Techniques Handbook.
When people talk about 'idioms' they usually mean one-
or two-line snippets like the one fastolfe mentioned
that pre-extends a hash.
But PATH isn't going to be about that at all.
The idea of PATH is that there are a lot of powerful programming techniques
that are possible in Perl but not in other languages that Perl programmers are familiar
with. Since Perl programmers haven't seen these techniques before,
they don't know how to use them, what they are good for, or even that they
exist, and they are letting a lot of the power and expressiveness of Perl go to waste.
The techniques are not little things like pre-extending a hash.
They are much bigger ideas that apply to the organization of entire
programs, ideas on the scale of 'object-oriented programming'.
One example is the idea that in Perl you can write a function that
manufactures other functions. Instead of writing a lot of similar functions
in the source code, you instead write one function which, when
called, generates the function that you actually want to use and returns it.
By invoking this 'function factory' with different arguments, your program
can manufacture as many functions as it needs to without your having to guess
in advance what all the functions will need to do.
Perl's own sort operator is a limited example of this.
If sort only sorted lists alphabetically, it would only
bone ten-thousandth as useful as it is. But instead, it gets an
argument, supplied by the programmer, which tells it how to compare
two list elements. In effect, this extra argument transforms sort into a
different function, which sorts lists in the way that the
programmer specified; if you give it a different argument, you get a
different kind of sorting function back out.
This is tremendously useful in the case of sort,
but most Perl programmers don't realize that they can apply the same techniques
to their own functions in many similar circumstances and
make their own functions much more useful and general than
they would have been otherwise.
Anyway, if you're interested, the correct URL is
http://perl.plover.com/book/.
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Mine wouldn't be a link to PerlMonks.org. ;)
Maybe it doesn't. I don't know -- I've never heard of this
handbook of which you speak. I have heard a couple of his
talks on the matter. So if he's making a compedium of them,
that would be super.
$_="goto+F.print+chop;\n=yhpaj";F1:eval
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RE: Efficient Perl Programming
by Dominus (Parson) on Nov 11, 2000 at 19:15 UTC
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You may want to take a look at
Optimization
of Computer Programs in C. It's ostensibly about C, but
actually most of the optimization techniques it discusses
(such as loop expression hoisting) are applicable in
any language, including Perl.
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Re: Efficient Perl Programming
by metaperl (Curate) on Nov 09, 2000 at 20:34 UTC
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http://perl.plover.com/book/
is the URL to MJD's book-in-progess: "Perl Advanced Techniques Handbook"
Also, are you going to wait until Perl 6 to write this book?
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