Python log the lines which returned the value in a callable

trace_return.py

def trace_return(pretty_printer):
    def decorator(fun):
        def decorated(*args, **kwargs):
            import sys
            import inspect

            last_line = None
            entered = False

            def tracer(frame, event, arg=None):
                nonlocal last_line
                nonlocal entered

                if event == 'call':
                    if not entered:

                        entered = True
                        return tracer
                    else:
                        return None
                elif event == 'line':
                    frame_info = inspect.getframeinfo(frame)

                    last_line = (frame_info.filename, frame_info.lineno)
                    return tracer
                elif event == 'return':
                    return
                elif event == 'exception':
                    return tracer
                else:
                    raise NotImplementedError(repr(event))

            old_tracer = sys.gettrace()
            sys.settrace(tracer)
            rtn = fun(*args, **kwargs)
            sys.settrace(old_tracer)
            import pprint
            pprint.pprint([
                fun.__name__,
                pretty_printer(args, kwargs, rtn),
                last_line
            ])

            return rtn
        return decorated
    return decorator

@trace_return(lambda @trace_return(lambda args, kwargs, rtn: [kwargs['date'], rtn])
def fun(date):
    return date