# file P1.pm
package P1;
sub new { my $class = shift; return bless {} => $class }
sub A1 { print "i am A1 in P1\n"; }
sub A2 { print "i am A2 in P1\n"; }
1;

##</code><code>##

# file P2.pm
package P2;

use parent 'P1';

sub new { my $class = shift; return bless {} => $class }

sub A1 { print "i am A1 in >>>P2<<< (i have overwritten previous A1)\n"; }
# A2 and everything else are inherited from class P1
1;

##</code><code>##

# file test.pl
# run: perl -I. test.pl
use P2; # and not P1

my $P2obj = P2->new();

$P2obj->A1(); # this is overwritten
$P2obj->A2(); # this is inherited verbatim from parent P1