import sys

def tracer(frame, event, arg):
    if event == 'call':
        print(event, frame.f_code.co_name,
                'with count', frame.f_locals['count'])
        if frame.f_locals['count'] > 0:
            print('returning None: the scope shouldn’t be traced')
            return None
    else:
        print(event)
    return tracer

def gen(count):
    count += 1
    yield count
    yield count

it = gen(int(sys.argv[1]))
sys.settrace(tracer)
next(it)
next(it)
sys.settrace(None)