No definitive answer, but educated guess: I'm not sure how things are in Ruby, but in Python frame object lifetime does not correspond to the C stack implementi

No definitive answer, but educated guess: I'm not sure how things are in Ruby, but in Python frame object lifetime does not correspond to the C stack implementing the interpreter. If your code throws an exception, frames are returned as part of the public API of the exception object, and can thus indefinitely outlive the associated function execution. You could still implement an array-oriented frame stack in Python, but I think that would mean exceptions become more expensive, as it means making a complete copy of the array any time an exception was thrown, even if the user never makes use of it.