I was recently looking at the source of a wxPython-based GUI application, about 45.5KLOC in size, not counting the libraries used (e.g. Twisted). The code was written by Java developers who are relatively new to Python, and it suffers from some performance issues (like a 30-second startup time). In examining the code, I found that they had done lots of things that make sense in Java, but which suck terribly in Python. Not because “Python is slower than Java”, but because there are easier ways to accomplish the same goals in Python, that wouldn’t even be possible in Java.
So, the sad thing is that these poor folks worked much, much harder than they needed to, in order to produce much more code than they needed to write, that then performs much more slowly than the equivalent idiomatic Python would.
Source: Python Is Not Java, an article by PJ Eby.