I agree about Python's libraries. Normally, I'm a Ruby programmer, because I like Ruby's syntax and the Rack/Rails/Sinatra web stack.
But if I need to do scientific or linguistic programming, Python is absolutely amazing. SciPy, NumPy, Matplotlib and NLTK support a rich and deep ecosystem. And it's vastly nicer programming environment than Matlab and Octave.
(Of course, GNU R is also pretty useful if you're doing pure statistics.)
Same here. I used to do a lot of Python programming, but moved to Ruby because of Rails. When I had to work on a machine learning paper, I spent weeks looking for a equivalent to NumPy or Matplotlib in the Ruby world, but nothing comes even close!
IMHO, languages matter less than the available libraries, and in my experience only Java matches the depth of the Python ecosystem.
That Python is a nice language to work with, that's just a bonus.