The maintainers implemented enhancements in both 3.x and 2.x for many years. Eventually they got tired of it. Version 2.7 corresponds to 3.4. The reason why 3.5

The maintainers implemented enhancements in both 3.x and 2.x for many years. Eventually they got tired of it. Version 2.7 corresponds to 3.4. The reason why 3.5 is the first 3.x that started to gain a following was that Guido announced there'd be no 2.8. You could argue that the reason folks didn't adopt 3.x quickly was that the core devs stayed committed to 2.x. It's standard practice for software maintenance to work on both the old version and the new fork for a while, giving users a chance to switch. Look at how Microsoft manages versions of Windows. I think the Python devs stand out in their willingness to work on both versions for so long.