15 Exercises to Know A Programming Language

[Martin]

I am trying to improve my Python skills through some exercises.
Currently I am working on Larry's "15 exercises to know a programming
language " (http://www.knowing.net/
PermaLink,guid,f3b9ba36-848e-43f8-9caa-232ec216192d.aspx). The first
exercise is this:

"Write a program that takes as its first argument one of the words
'sum,' 'product,' 'mean,' or 'sqrt'  and for further arguments a
series of numbers. The program applies the appropriate function to
the series."

My solution so far is this:

http://dpaste.com/13469/

I would really like some feedback. Is this a good solution? is it
efficient? robust? what could be improved? any not looking for a
revised solution, hints on what to improve are also very welcome.

Martin