Interestingly, the Python code fails if w1 contains characters outside of PCHR. Therefore, using only valid characters the following should work:

#!/usr/bin/perl
use warnings;
use strict;
use feature qw{ say };

my @pchr = qw( K Q R B N P );
my $w1   = 'QRKPNBQ';  # <- Q is repeated!
my $w2 = join "", map $_ x (() = $w1 =~ /$_/g), @pchr;
say "$w1 \-> $w2";
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