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Keyboard input: let the player take control

A game you can't control is just a cartoon. The moment a key moves something on screen, you're playing. Two small commands make that happen.

The big idea

key_held("left") is True on every frame the key is down. key_pressed("space") is True only on the one frame the key goes down.

See it in code

1Start simple

play() runs every frame. So ask about the key every frame. While it's held, move the basket a little:

python
basket = Thing(x=320, y=420, width=100, height=24, color="teal")
basket_speed = 6

def play():
    if key_held("right"):
        basket.x = basket.x + basket_speed

def draw():
    paper("misty rose")
    rect(x=320, y=455, width=640, height=50, color="burlywood")
    basket.draw()
The right arrow was held for half a second:
A bakery scene where a teal basket has slid to the right of the center, above a wooden counter.

The key was down for 30 frames. Six steps on each frame makes 180 steps in all. Held keys are for steering.

2A step further

A piece doesn't know where the screen ends. Check its edge on every frame, and push it back if it has gone too far:

python
basket = Thing(x=320, y=420, width=100, height=24, color="teal")
basket_speed = 6
half_basket = 50

def play():
    if key_held("left"):
        basket.x = basket.x - basket_speed
    if key_held("right"):
        basket.x = basket.x + basket_speed
    if basket.left < 0:
        basket.x = half_basket
    if basket.right > WIDTH:
        basket.x = WIDTH - half_basket

def draw():
    paper("misty rose")
    rect(x=320, y=455, width=640, height=50, color="burlywood")
    basket.draw()
The left arrow was held the whole time, and the wall stopped the basket:
A bakery scene where a teal basket is pressed against the left edge of the screen, stopped by the wall.

basket.left is the basket's left edge. When it slips below 0, the basket is put back with its edge exactly on the wall.

3In the arcade

For a jump or a zap, you want one action per tap. That's key_pressed. This game counts both kinds, so you can see the difference:

python
game.taps = 0
game.held = 0

def play():
    if key_pressed("space"):
        game.taps = game.taps + 1
    if key_held("space"):
        game.held = game.held + 1

def draw():
    paper("midnight blue")
    write(f"Taps: {game.taps}", x=320, y=190, size=72, color="gold")
    write(f"Frames held: {game.held}", x=320, y=280, size=44, color="white")
Space was tapped three times and held down for a second:
A dark blue game window showing "Taps: 3" in large gold text and "Frames held: 60" in white text below it.

Three taps counted as 3. The same key, held, counted 60 times. Use the wrong one for a jump and your bird turns into a rocket.

The same idea, everywhere

Every control in every game is one of these two. Steering, sliding, and aiming use a held key. Jumping, serving, and firing use a pressed key.

Try it yourself

In the wall game, change basket_speed to 12 and try it. Then add two more lines so the "a" and "d" keys steer as well as the arrows.

The common mistake

Misspelling a key's name. key_held("Right arrow") isn't a name the game knows, and it tells you so. The names are short: "left", "right", "up", "down", "space", or a letter.

What it unlocks

Keys are checked inside the game loop. They change a game piece, and each check is an if.

Related concepts