I agree, that is the one the (relative) dangers when you are proficient in a language; it is so much easier and faster to write something in the language you already know, rather than having to learn everything from scratch. Of course, it also depends on how much difference there is between old and new languages; a Python expert could probably pick up Ruby in no time, and vice versa; but Python vs Haskell is a different story.
Yeah, Python is my Blub. I know I should learn stuff like Haskell and Clojure, but I just haven't come across any cases where it's more than a minor inconvenience to make Python do what I need.
