I'm thinking about learning ruby and python a little bit, and it occurred to me, for what ruby/python is good for? When to use ruby and when python, or for what ruby/python is not for? :)
What should I do in these languages?
thanks
To avoid the holy war and maybe give another perspective I say (without requesting more information of what fun part of programming the question-ere thinks is cool to do):
Learn python first! 
If you haven't done any scripting language yet I would recommend python.
The core of python is somewhat cleaner than the core of ruby and if you learn the basic core of scripting with python first you will more or less as a bonus learn ruby.
You will (because you use python) write code that looks very clean and has good indentation
right from the beginning. 
The difficulties about what to learn is what you actually   will you try to solve!
If you are looking for a new production language to solve X the answer get more complicated.
Is X part of the language core? Was the language in fact invented to solve X?
If the question was: What single programming language should I Master and eventually reach Nirva with? My answer is, I don't have a clue! 
(CLisp, Scheme48, Erlang or Haskell should probably have been on my final list though)
PS.
I know that this isn't the spot on answer to the very simplified question in the post.
what can ruby do that python can't or what can python do that ruby can't.
The point is that when you set out to learn something one usually have a hidden agenda so you try to solve your favorite problem in any language again and again.
If your really are out to learn without have an agenda I think that python in it's most basic form is a clean and crisp way and you should be able to use the same style when using ruby. 
DISCLAIMER: I prefer ruby in a production (commercial setup) over python.  I prefer ruby over python on windows.  I prefer ruby over python on the things I do at home. I do that because the things I really like to solve is more fun to solve in ruby than in python.  My programming style/habit tends to fit better in ruby.
python and ruby - for what to use it?