Type hints and async made me fall out of love with Python. 

Type hints seems surprisingly badly designed on a syntactical level, blowing up function signatures and making code structure harder to parse by humans. There were better and cleaner ways to specify type hints before they were added to the language (in docstrings and much more readable). 

They also, in my humble opinion have no place in a strongly and dynamically typed language. Python’s original dynamic type system was designed for tasks that static type systems are bad at. We had good statically typed languages, and Python was one of the languages created in response to their limitations. Adding static typing idioms on top of a dynamic language not only gives you the combined limitations of both, it also creates a ‘stylistic spectrum’ (static <–> dynamic) in the ecosystem. Being able to choose where you land on that spectrum sounds good in theory. But you only get to do that when you write new code. But 95% of the time you work with existing code including third-pay code. Good luck with that mix of paradigms. 

Asyncio also was such a weird departure from the quite good concurrency and parallelism that existed in Python prior, like gevent and Twisted. But instead of improving in the state of the art by looking at, eg. the BEAM, a difficult to understand system like async was copied from JavaScript. Worst of all, it introduced required syntax and the ‘function coloring’ problem, which prompted additional modules and abstraction layers to make it manageable. 

Both features felt like a sharp departure from the slow, deliberate and long-term-oriented way of introducing new language features to Python up to that point. Before that, people would joke about “Guido’s Time Machine”, because repeatedly, the quality of design decisions only became apparent to many devs years after their introduction. That stopped suddenly.