Without using every feature you still have to conform to the complexity of the runtime. Every variable in that loop is a hash map lookup into the locals. `np.linalg.norm` is two field accesses, necessitating more hash map lookups on the module objects. `-` and `<` are attribute lookups as well as full function calls.

> Every variable in that loop is a hash map lookup into the locals.

No, it's a LOAD_FAST bytecode instruction. (The other stuff is mostly right, and probably contributes.)