If you didn't know, Perl is another very popular, free and open source interpreted language.
If you have ever tried writing a large program in Perl, you would have answered this question yourself! Perl programs are easy when they are small and simple, but they quickly become unwieldy once you start writing bigger programs. When compared with Perl, programs written in Python are definitely simpler, clearer, easier to write and hence more understandable and maintainable. I do admire Perl and I still use it (especially for my website), but whenever I write a program, I always think in terms of Python. Too much hacking and changes have made Perl very complicated and confusing. However, the upcoming Perl6 might do something about this but that is still a long way off.
The only significant advantage that Perl has is its library called CPAN - the Comprehensive Perl Archive Network. As the name suggests, this is a humongous collection of Perl modules and is mind-boggling because of its sheer size and depth - you can do virtually anything you can do with a computer using these modules. One of the reasons that Perl has a better library than Python is that it has been around for a much longer time than Python.
Also, the new Parrot virtual machine is designed to run both the completely redesigned Perl6 as well as Python and other interpreted languages like Ruby, PHP and Tcl. What this means to you is that maybe you will be able to use all Perl modules from Python in the future, so that you will have the best of both worlds - the powerful CPAN library combined with the powerful Python language. However, we will just have to wait and see what happens.