# up_down.py

# up_down.py

def up_down(lowest_value, highest_value, step=1, current='void'):
    if current == 'void':
        current = lowest_value
    while True: # Begin infinite loop
        yield current
        current += step
        if current <= lowest_value or current >= highest_value:
            step *= -1 # Turn around when either limit is hit

test = up_down(-5, 10)
count = 0
for j in test:
    print(j) # for demonstration purposes
    count += 1
    if count >= 50: # your ending condition here
        break