Question

What is a good way to implement keyboard handling? In any language, where I write a keyboard-interactive program (such as a tetris game), I end up having some code that looks like this:

for event in pygame.event.get():     if event.type == KEYDOWN:         if False: pass          #make everything an elif         elif rotating: pass         elif event.key == K_q:         elif event.key == K_e:         elif event.key == K_LEFT:             curpiece.shift(-1, 0)             shadowpiece = curpiece.clone(); setupshadow(shadowpiece)         elif event.key == K_RIGHT:             curpiece.shift(1, 0)             shadowpiece = curpiece.clone(); setupshadow(shadowpiece) 

(shortened). I don’t like this, as this has to go in my main loop, and it messes with all parts of the program. This also makes it impossible to have a user config screen where they can change which key maps to which action. Is there a good pattern to do this using some form of function callbacks?

Answer 1

You could create a dictionary where the keys are the input and the value is a function that handles the keypress:

def handle_quit():   quit()  def handle_left():     curpiece.shift(-1, 0)     shadowpiece = curpiece.clone(); setupshadow(shadowpiece)  def handle_right():     curpiece.shift(1, 0)     shadowpiece = curpiece.clone(); setupshadow(shadowpiece)  def handle_pause():     if not paused:         paused = True  branch = {   K_q: handle_quit   K_e: handle_pause   K_LEFT: handle_left   K_RIGHT: handle_right }  for event in pygame.event.get():     if event.type == KEYDOWN:         branch[event.key]() 

Then changing the keys is a matter of modifying keys of the dictionary.