Here is a study of how lines of code produced annually differs across languages in a collection of open-source projects: http://sequoia.cs.byu.edu/files/pubs/Delorey2007.pdf
Of course, the correlation between lines of code and "productivity" is pretty nebulous. (Copy-and-paste programming is the most obvious example of a negative correlation.) LoC is an easy thing to measure, but not necessarily useful.
Python is generally considered to be 2 or 3 times as expressive as Java. I did some estimation on a compiler implementation in C++ and arrived at the conclusion that it could have been done in 20% as much Python.
(FWIW, OCaml is probably a better language for compiler writing. It hits all its strengths. Failing that, I'd still rather do one in Python or Lua than C, though.)
I didn't say anything about the intelligence of Java programmers. Like everywhere else some are brilliant and some are dumb as hammers. When I said "everything is too damned complicated", I was thinking of Java Web development which has a proliferation of one-size-fits-all frameworks which encourage bloated implementations. It could be that I have blundered into a tiny swamp and everywhere else is sweetness and light, but I dont think so.
For example, I would much rather maintain a Java-based web application than a PHP-based web application.
Says who? Ignoring the fact that LoC is a terrible metric for measuring anything except the amount of paper it would require to print the program, I think it would be very hard to use it to quantify how much you will accomplish. Your (implied) assertion that you will not just accomplish less, but accomplish between a half and a fifth as much in Java as in Python is even more outlandish. I can't imagine you have any evidence to support this?
> Stay away from Java; everything is too damned complicated
What is this supposed to mean? That the hundreds of thousands of people who make their livings from doing web development with Java and being competent Java programmers are either stupid (for not programming in Python), or super-smart (because they can grok Java)? This is pretty absurd. Java is no better and no worse than pretty much any other language in wide-spread use. To its benefit, it has extensive library support for pretty much everything under the sun, and all the enterprise features which would make it relatively painless to do a whole heap of things that would become very difficult in almost any other language.
Really, I think you should refrain from giving advice on specific programming languages if you are just going to resort to complete and utter nonsense to provide comparisons.