Idea: Simpler and More Expressive Type Annotations

[Jelle (Jelle Zijlstra)]

@ImogenBits

we could also think about not using ast.AST objects directly in order to skip their construction and/or write the evaluating code in C

The Python-level AST objects are relatively expensive. Dino opened an issue about improving this (Have internal immutable AST nodes · Issue #140514 · python/cpython · GitHub) but not sure when or if that will land.

@ImogenBits

and/or write the evaluating code in C

It might make sense to have a separate third-party library that evaluates annotations in C (or Rust?) for speed, so we can keep the standard library implementation relatively simple but users like Pydantic that care about speed can use a faster version. Such a library could also allow backporting new syntax to earlier versions of CPython.

@ImogenBits

On the topic of memory usage, I suspect that the impact will be reasonably small. The AST is stored as tuples which almost exclusively contain statically allocated strings and integers, so it really shouldn’t be more than a handful of pointers per annotation.

I wouldn’t be so sure. Memory usage was a major motivation for PEP 563 and 649: people were noticing significant memory usage from typing objects, and those weren’t huge either.