Adding a new Method to a Package

Suppose you're using someone else's package
There's a method you wish it has, but it doesn't
For example:

         my $sth = $dbh->query(...);
         error() unless defined $sth;

         my $num_records = $sth->numrows();
         for ($i=0; $i<$num_records; $i++) {
           # Get next record
           my %data = $sth->fetchhash();

           # Do something with %data
         }

You're sick of repeating the same error-checking code
You wish that $dbh supported a myquery method