Press Key Only Once in Pygame - count

Question

I'm trying to do a pathfinding algorithm visualizer and I want that by pressing the S key you will put a start node depending on where your mouse is located but I want the player to only be able to do it once until he chooses to clear the board and he can put another start node since the board is empty so that he doesn't have multiple start nodes on a single grid and I tried doing it with keeping track of a count variable but it didn't work it still allowed to press multiple times(I'm not talking about KEYDOWN and KEYUP, I want the player to press it only once and not be able to do it more times). If possible can someone tell me how to allow to put only one start node at each board but when board is cleared and empty you can put once again but also only one start node.
snippet of my code attempt:
start_count = 0
if event.type == pygame.KEYDOWN:
if event.key == pygame.K_s and start_count < 1:
for node in nodes_list:
node.draw_start_node()
start_count += 1

Answer 1

You need to initialize start_count once before the application loop, instead of continuously in the application loop:
start_count = 0
while True:
# [...]
for event in pygame.event.get():
if event.type == pygame.KEYDOWN:
if event.key == pygame.K_s and start_count < 1:
for node in nodes_list:
node.draw_start_node()
start_count += 1
# [...]