week09.py

# Week 9: Move the Hero (Keyboard Events)
# Goal: Use keyboard events to control a turtle with arrow keys
# This is the foundation for keyboard-controlled games!

import turtle

# Setup screen with specific size
screen = turtle.Screen()
screen.title("Move the Hero")
screen.setup(width=600, height=400)

# Create hero turtle
hero = turtle.Turtle()
hero.shape("turtle")  # Built-in shapes: "turtle", "square", "circle", "arrow"
hero.penup()          # Don't draw lines when moving
hero.speed(0)         # Instant movement (looks smooth)

# CONSTANT: how far to move with each key press
STEP = 20  # Try changing this! Bigger = faster movement

# ===== Movement Functions (Event Handlers) =====
# Each function is called when the corresponding arrow key is pressed

def up():
    """Move hero up by STEP pixels"""
    hero.sety(hero.ycor() + STEP)  # ycor() gets current Y, add STEP to move up

def down():
    """Move hero down by STEP pixels"""
    hero.sety(hero.ycor() - STEP)  # Subtract to move down

def left():
    """Move hero left by STEP pixels"""
    hero.setx(hero.xcor() - STEP)  # xcor() gets current X, subtract to move left

def right():
    """Move hero right by STEP pixels"""
    hero.setx(hero.xcor() + STEP)  # Add to move right

# ===== Connect Keys to Functions =====
# This is called EVENT BINDING - connect events to handlers

screen.listen()  # Tell screen to listen for keyboard events (MUST do this first!)

# onkey(function, key_name) connects key press to function
# Important: Pass function NAME without (), otherwise it runs immediately!
screen.onkey(up, "Up")       # Up arrow key → call up()
screen.onkey(down, "Down")   # Down arrow key → call down()
screen.onkey(left, "Left")   # Left arrow key → call left()
screen.onkey(right, "Right") # Right arrow key → call right()

# ===== Coordinate System Reference =====
# Center of screen is (0, 0)
#         +Y (up)
#          |
#  -X -----+----- +X (right)
#  (left)  |
#         -Y (down)

# Keep window open
screen.mainloop()