Mutable types are hiding everywhere — even in functions In Python, you can define functions with optional arguments — that is, arguments that you don’t need to state explicitly afterwards ...

These dynamically typed objects are referred to as mutable, ... Anyway, objects under Python are a complex world that space prevents us from exploring in any greater detail.

PyO3 provides a way to hold the GIL by way of Rust’s lifetimes mechanism, which gives you a way to take either mutable or shared access to Python objects. Different object types have different ...

Any mutable Python object doesn’t have a consistent hash value over its lifetime, and so can’t be used as a key. For instance, a list can’t be a key, ...