Moving to the beginning of a function

REVEN v2.9.0
from reven2.trace import Transition
from typing import Tuple, Optional

def call_bounds(tr: Transition) -> Tuple[Optional[Transition], Optional[Transition]]:
    Given a transition anywhere inside of a function, this function returns
    the transition at the beginning of the function call and the transition at
    the end of the function call.
    return (tr.step_out(is_forward=False), tr.step_out(is_forward=True))