If event.button == 1:
Print("Left button is pressed")
event.button can equal several integer values:
1 - left click
2 - middle click
3 - right click
4 - scroll up
5 - scroll down
Instead of an event, you can get the current button state as well:
pygame.mouse.get_pressed()
This returns a tuple:
(leftclick, middleclick, rightclick)
#all values are Boolean
Each one is a boolean integer representing button up/down.
You can do like this:
Left, scroll,right = pygame.mouse.get_pressed()
Reset all three values once event handling is done. You can even store for scroll too.
Eg: left, scroll , right, scrollup , scrolldown = pygame.mouse.get_pressed()