[reuser]

There is no Pope of Python to tell you "you can't write new code to do xyz, because someone else is already working on that."

How would that be enforced? Would someone's Python privileges be taken away?

What if the person working on xyz was inactive for a while? What if their xyz had a problem and they didn't want to fix it?

The "obvious way to do it" does not and was never, ever intended to bind anyone's hands from writing a library or app similar to something someone else wrote. It is a principle of language design, that it should give SOME consideration to readability and learnability rather than giving 100% of everything to nifty obscure features that help you write awesomely clever executable line noise.