> What's use of Python 2 if you can't use libraries[1]?
Unless some python 3 fanatic goes out of his way to write a python 2 library deleting virus the existing code wont disappear. Also some of these pledges only limit feature releases, afaik numpy planned to still provide a long term support version with bugfixes for python 2. It also helps that python already comes with a lot of build in bells and whistles so third party libraries aren't always necessary either.
Sorry I wasn't clear nothing happens if your application doesn't change, but if you do sooner or later you'll be forced to upgrade your dependencies (could be a bug that you just found, maybe a bug, or maybe a performance improvement) if the updated version won't work on your python it will be tough. You'll have choice to either migrate your app to python 3 or fork the library and backport fixes.
You might be lucky and someone else might do that for you, but it will be harder and harder with time. Already according to JetBrains survey in 2019 (I believe) about 80% of people surveyed they already use python 3.
As for numpy I just checked[1] and the only wheels they are providing for the latest version are 3.5+ the package also says that it is 3 only.
Unless some python 3 fanatic goes out of his way to write a python 2 library deleting virus the existing code wont disappear. Also some of these pledges only limit feature releases, afaik numpy planned to still provide a long term support version with bugfixes for python 2. It also helps that python already comes with a lot of build in bells and whistles so third party libraries aren't always necessary either.