The issue here is that that definition of "safe" language basically excludes all practical languages, including languages like Python, because FFI is possible.

The issue here is that that definition of "safe" language basically excludes all practical languages, including languages like Python, because FFI is possible. In general when talking about safety in a language it's about the level of explicitness required to trigger unsafety. I like the distinction made in the nomicon (https://doc.rust-lang.org/stable/nomicon/meet-safe-and-unsafe.html https://doc.rust-lang.org/stable/nomicon/meet-safe-and-unsaf...) -- Rust comprises of two distinct languages. You have everyday Rust, which is completely memory safe, and "unsafe Rust", which looks similar to everyday Rust but is not safe. `unsafe {}` blocks are your FFI between the two. Looking at unsafe blocks as FFI is IMO a very useful mental model especially for understanding the changes to invariants involved.