How to detect key being held down in pygame

Question

I am trying to make a game using PyGame that has left and right movement on the a/d keys. I have got this code but it will only detect a key down not a key hold:

        if event.type == pygame.KEYDOWN:
            if event.key == pygame.K_SPACE:
                if onPlatform == True:
                    onPlatform = False
                    ytarget = ylevel + 100
            if event.key == pygame.K_a:
                print("a")
                xlevel = xlevel-2
            if event.key == pygame.K_d:
                xlevel = xlevel+2

I would like to use the pygame.key.get_pressed() method but I can't get it to work.

Note: this question: Pygame- detect if a key is held down? does not answer my question so please don't mark this as a duplicate of that, If you do find another answer though, please direct me there:)