Because with JVM languages, and their &quot;horrid&quot; backwards compatibility (that everyone always loves to bash), I can declare dependencies on libraries written in Java 1.1, and it will <i>JUST WORK</i>.<p>From what I understand, there&#x27;s a fairly large chasm between Python 2&#x2F;3 (such that a lot of people use external libraries to deal with coding cross-compatibile code, and apparently get wrong some-times).