Both these languages seem extremely similar to me. Although Python supports actual classes instead of being prototype-based, in Python classes are not all that different from f
Being a JavaScript developer and done some Python stuff (thanks to Google App Engine) I would say that the two major differences between JavaScript and Python would be
Formatting. JavaScript doesn't care about the looks of your code (think of all the code minimizers and what the resulting looks like)
Unicode support. JavaScript is all the way unicode, GAE's Python 2.5 not so much (having Latin 1 as the default character set). So having the need to support non-latin characters can be a real PITA if your'e not sure what you are doing.