drmikec has asked for the wisdom of the Perl Monks concerning the following question:

Hello all,
I wrote a script to condense a very large XML file with XML::Twig on ActivePerl 5.6.1 - worked great! I upgraded to ActivePerl 5.8.8 and it broke with 
"Can't call method "flush" on an undefined value at C:/Perl/site/lib/X
+ML/Twig.pm
line 6832, <INFILE> line 4083."

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Here is the offending section, it breaks with the first flush(): 
select \*OUTFILE;
my $t = new XML::Twig( twig_roots => {
#                                      'MemberID' => \&member,
                                      'Aging' => \&balance,
                                        'Transaction' => \&transaction
+,
                                        'Line' => \&line,
                                        'Chits' => \&chits},
                      pretty_print => 'indented',
                      twig_print_outside_roots => \*OUTFILE,          
+     # print the rest
);

$t -> parsefile ("temp.xml");
<snip>
sub balance {
    my ($t, $balance) = @_ ;
    my %balance;
    $balance{30} = $balance->field( 'BAL_30' );
    $balance{60} = $balance->field( 'BAL_60' );
    $balance{90} = $balance->field( 'BAL_90' );
    $balance{120} = $balance->field( 'BAL_120' );
    $balance{150} = $balance->field( 'BAL_150' );
    $balance{180} = $balance->field( 'BAL_180' );
    local ($balance90, $balance120, $balance150, $balance180);
    $balance30 = $balance{30};
    $balance60 = $balance{60};
    $balance90 = $balance{90};
    $balance120 = $balance{120};
    $balance150 = $balance{150};
    $balance180 = $balance{180};
    local $balancelate = ($balance90 + $balance120 + $balance150 + $ba
+lance180);
    $balancelate =$rounder->round($balancelate);
    $balance->delete(90);
    $balance->delete(120);
    $balance->delete(150);
    $balance->delete(180);
    my $balance30elt = new XML::Twig::Elt('BAL_30', $balance30);
    $balance30elt->set_text($balance30);
    $balance30elt->set_att(Period => 1);
    $balance30elt->paste('first_child', $balance);
    my $balance60elt = new XML::Twig::Elt('BAL_60', $balance60);
    $balance60elt->set_text($balance60);
    $balance60elt->set_att(Period => 2);
    $balance60elt->paste('last_child', $balance);
    my $balance90 = new XML::Twig::Elt('BAL_90', "$balancelate");
    $balance90->set_text( "$balancelate" );
    $balance90->set_att(Period => 3);
    $balance90->paste('last_child', $balance);
    $balance -> flush(\*OUTFILE);
}

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I want to use WxPerl to put a nice Windows wrapper around it, so I need the 5.8.x. Any help or insight would be greatly appreciated! -Mike

Edited by planetscape - removed pre tags, replaced with code tags

Replies are listed 'Best First'.
Re: XML-Twig - AS5.6.1 vs AS 5.8.8
by runrig (Abbot) on Mar 29, 2006 at 00:34 UTC
    $element->delete() does not take an argument, it deletes the element itself, I think you intend for those deletes to be more like (this takes care of all in one go):
    # Delete BAL_* nodes
$balance->cut_children(qr/^BAL_\d+$/);

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    Note also that you are not deleting the BAL_30 and BAL_60 nodes, so you end up with two each of those (the originals and the ones you create with attributes). The cut_children() above assumes you didn't want the duplicates.
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Re: XML-Twig - AS5.6.1 vs AS 5.8.8
by mirod (Canon) on Mar 29, 2006 at 08:09 UTC

    There are a few problems with your code:

    • first, as mentionned by runrig, you delete $balance and then you flush it. So $balance is deleted, and becomes undef-ed, so you can't call a method on it (are you sure this code worked in 5.6.1?)
    • you do a couple of times things like this: 
          my $balance30elt = new XML::Twig::Elt('BAL_30', $balance30);
    $balance30elt->set_text($balance30);
    $balance30elt->set_att(Period => 1);
    $balance30elt->paste('first_child', $balance);

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      The set_text is completely useless (you set the text in the new above, and BTW new XML::Twig::Elt is a deprecated way of calling a method, XML::Twig::Elt->new is the proper way.
      In any case, you can replace all those lines by the more compact 
          $balance->insert_new_elt( first_child,     # position
                              'BAL_30',        # tag
                              { Period => 1 }, # attributes
                              $balance,        # content
                            );

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      And actually it looks like you don't even need to delete then re-create the BAL_30 (and BAL_60) element. You could just do: 
         $balance->first_child( 'BAL_30') # get the element
           ->del_atts               # if it had atts originally
           ->set_att( Period => 1)
           ;

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    Does it make sense?

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      Yes, it does. Thanks, Michael. I implemented the method calls as you suggested, and it works, except for one small thing - the first time $balance->flush; is called, it writes a <Root> tag immediately preceding the <Aging> tag. As you can surmise, I'm processing a member billing file, and it doesn't write the <Root> tag on subsequent members, just the first one. I can hack my way around it, but I don't understand why it is happening. Thanks. -Mike
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        A minimal test case with data would be helpful. Do you mean that each Aging element is a child of a different Root element? And that the parent element of your entire document is some other-named sort of "root" element? Or that all of your Aging elements are children of one Root element (in which case it sounds like it's behaving correctly)?
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