Just a small note about mypy and python - annotations are first-class citizens in Python3 and are not tied to any particular type checking system such as mypy, but are instead a core part of the language and actually serve vital functions in frameworks and libraries that are used to check interfaces such as Pydantic and FastAPI (eg URL params).
Mypy is just one type checker for Python, but there are many others including pyright. In fact pyright is quickly becoming the dominant checker over mypy.
Am I right in thinking that Python's type annotation syntax originally came from Mypy though?
IIRC Mypy started off as a type annotation syntax and corresponding type checker for Python. Mypy's type annotations were adopted by Python itself (in version 3.5 - PEP 484), which reduced Mypy's role to be just a type checker.
Since then, type annotations have indeed become a core part of Python - not only are they used in frameworks and libraries, but are also required to use language features like @dataclass.
No, Python's current type annotation syntax was added in Python 3.0 as a generic annotation syntax, in the hope that somebody else might come along and build a type-checker or other tooling on top:
https://peps.python.org/pep-3107/
MyPy was one such tool, and I think it had conventions for adding type annotations in comments, in places where Python didn't yet support them (such as variable assignment), but I'm pretty sure it was never a TypeScript-style pre-processor - type-annotated programs always ran directly in the unmodified CPython interpreter.