Math not working
in [Perl]
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From: Faith Greenwood on 6 Feb 2010 15:13 I'm very confused. I'm pulling some numbers from an xml file and then trying to do some math. ####XML File <library> <books>5</books> <pages>12</pages> </library> ####Code #!/usr/bin/perl use strict; use warnings; use XML::LibXML; use XML::XPath; my $parser=XML::LibXML->new(); my $doc=$parser->parse_file("C:/scripts/production/xml.xml"); my $books=$doc->find("//books/text()"); my $pages=$doc->find("//pages/text()"); print "$books\n"; print "$pages\n"; my $total_pages=$books * $pages; ######################## when I run the above code, I get the output: 5 12 Operation "*": no method found, left argument in overloaded package XML::LibXML::Nodelist, right argument in overloaded package XML::LibXML::Nodelist at script.pl line 16 Why can't I do math operations here? thx!
From: John Bokma on 6 Feb 2010 16:40 Faith Greenwood <fgnowfg(a)gmail.com> writes: > my $total_pages=$books * $pages; > ######################## > when I run the above code, I get the output: > > 5 > 12 > Operation "*": no method found, > left argument in overloaded package XML::LibXML::Nodelist, > right argument in overloaded package XML::LibXML::Nodelist at > script.pl line 16 You are trying to multiply two Nodelists... > Why can't I do math operations here? that's why. You probably have to 1) check that each nodelist has one item and 2) extract the text out of each node 3) multiply the text (which Perl will automagically convert to numbers) -- John Bokma j3b Hacking & Hiking in Mexico - http://johnbokma.com/ http://castleamber.com/ - Perl & Python Development
From: Daniel Molina Wegener on 6 Feb 2010 16:42 -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA512 On S�b 06 Feb 2010 17:13, Faith Greenwood wrote: > I'm very confused. I'm pulling some numbers from an xml file and then > trying to do some math. OK, no problem... > > ####XML File > <library> > <books>5</books> > <pages>12</pages> > </library> > > ####Code > #!/usr/bin/perl > use strict; > use warnings; > use XML::LibXML; > use XML::XPath; > > my $parser=XML::LibXML->new(); > my $doc=$parser->parse_file("C:/scripts/production/xml.xml"); > > my $books=$doc->find("//books/text()"); > my $pages=$doc->find("//pages/text()"); > > print "$books\n"; > print "$pages\n"; > > my $total_pages=$books * $pages; > ######################## > when I run the above code, I get the output: > > 5 > 12 > Operation "*": no method found, > left argument in overloaded package XML::LibXML::Nodelist, > right argument in overloaded package XML::LibXML::Nodelist at > script.pl line 16 Well, the error is clear. The /find()/ method returns a Nodelist object, so you are trying to miltiply $books and $pages which are both XML::LibXML::Nodelist objects. Try using something like: $books = int($books->string_value()); $pages = int($pages->string_value()); my $total_pages = $books * $pages; > > > > Why can't I do math operations here? > > thx! Best regards, - -- Daniel Molina Wegener <dmw [at] coder [dot] cl> Software Architect, System Programmer & Web Developer Phone: +1 (510) 629-4267 | Blog: http://coder.cl/ -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.9 (GNU/Linux) iQIcBAEBCgAGBQJLbeJSAAoJEHxqfq6Y4O5NsjYP/2oFCmorBcavKkk2yVOHz3Qe bOWlqiBlpw0oNsNniPFQ3n/tTFeCb/6yNHz/HiEnNsFJT0CL1l7HWjAL7tO/Lz9M IWoUIOeEfqqDP0s0e34HTfyY1gu8/6jSUCoMsiT319PVVq/Kffp1fP/agY351Hsl OWQkSYtDG+Q4wVIbLJ1Mxsmv/+H7YkWtRGXNmwjBllIhFYRJZmtzTKx4l3ErQ/Fe Abw2yjm9M1G9Cl0muwdNuv/QwVequ2tH+MnGKFl03ulXc0Qk/drJDCnoTk2Pseze 6bkSB94rAAMO990rVYaQglsC30x4FHzK2EaH4W5F/2Q/U/4MXWfEgXBZV2YZcLZJ N2Rnoa6uZVzlEtcwrGFaPnB1/HRpDSL8FaOTvUHYDrdr8auWmPGc9z6twvL9HbVM g4USyU999wlSJkMyGrjnzjlJb5DCLuueEia+3Cb4XyarVN7b2OHrjq4yFOXW0iTU /1rpzeAgP68QDs+jJ7JxCD8xXqZBcPTFiCWTxS5yN7DP76QXJNXu6K0SXiL8iY4y m1ts05A5+FgZgteFk0HmODhwsetRJ/5+U0BAorv1JlYptUB7W0Q0zVyik7lICPa4 2Cm2Yv2lsLrBLtPanzj+8W1xWSB+khLSb1AxIY7znvNoZGObpFTiMoC+RFNPriqX t3KjPZpRxkug3JkicZxw =tQzG -----END PGP SIGNATURE-----
From: Ben Morrow on 6 Feb 2010 16:42 Quoth Faith Greenwood <fgnowfg(a)gmail.com>: > I'm very confused. I'm pulling some numbers from an xml file and then > trying to do some math. > > ####XML File > <library> > <books>5</books> > <pages>12</pages> > </library> > > ####Code > #!/usr/bin/perl > use strict; > use warnings; > use XML::LibXML; > use XML::XPath; > > my $parser=XML::LibXML->new(); > my $doc=$parser->parse_file("C:/scripts/production/xml.xml"); > > my $books=$doc->find("//books/text()"); > my $pages=$doc->find("//pages/text()"); > > print "$books\n"; > print "$pages\n"; > > my $total_pages=$books * $pages; > ######################## > when I run the above code, I get the output: > > 5 > 12 > Operation "*": no method found, > left argument in overloaded package XML::LibXML::Nodelist, > right argument in overloaded package XML::LibXML::Nodelist at > script.pl line 16 If you add warn overload::StrVal($books); before the multiplication, you will see that the 'numbers' are actually objects with overloaded stringification. Since there is no "*" overload, and no "0+" overload, and 'fallback => 1' was not specified[1], perl has no way to perform the multiplication. You can work around this by explicitly stringifying first: $books = "$books"; # stringify overloaded object $pages = "$pages"; # "" my $total_pages = $books * $pages; The comment is important so that the next person to look at the code doesn't mutter 'perldoc -q quote' and remove the lines :). Ben [1] I consider the fact that fallback => 1 isn't the default to be a bug in the perl overloading system, but it's much too late to change that now. Apart from anything else, any new overloads (like the -X overload that will be in 5.12) must behave as though fallback=>1 were specified, for compatibility.
From: Ben Morrow on 6 Feb 2010 17:42
Quoth dmw(a)coder.cl: > -----BEGIN PGP SIGNED MESSAGE----- Please don't do that here. > Well, the error is clear. The /find()/ method returns a Nodelist > object, so you are trying to miltiply $books and $pages which are > both XML::LibXML::Nodelist objects. > > Try using something like: > > $books = int($books->string_value()); The 'int()' is unnecessary, and unclear (since it implies $books->string_value might be a float we wish to truncate to an integer), Ben |