This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
The semantics of Python and Java are very similar, and most of the data structures in the Java collections are either built into Python or available in libraries.
The biggest differences are syntax and dynamic typing. Python uses a minimal syntax that many people find very readable (although it might take getting used to). And with dynamic typing, you don't have to declare variables. Development time tends to be faster in Python, but the compiler can't catch as many errors for you.
For me as a teacher, the biggest difference is that Python is a better first language. I see more of my students succeeding, and doing cooler things, than when I was teaching in Java.