Python交互小游戏（四）：Memory——Mouse input，list methods，dictionaries

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1 Mouse Input

例 1：

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# Examples of mouse input

import simplegui
import math

# intialize globals
WIDTH = 450
HEIGHT = 300
ball_pos = [WIDTH / 2, HEIGHT / 2]
BALL_RADIUS = 15
ball_color = "Red"

# helper function
def distance(p, q):
    return math.sqrt( (p[0] - q[0]) ** 2 + (p[1] - q[1]) ** 2)

# define event handler for mouse click, draw
def click(pos):
    global ball_pos, ball_color
    if distance(pos, ball_pos) < BALL_RADIUS:
        ball_color = "Green"
    else:
        ball_pos = list(pos) # pos是一个tuple，而tuple不能被修改
        ball_color = "Red"

def draw(canvas):
    canvas.draw_circle(ball_pos, BALL_RADIUS, 1, "Black", ball_color)

# create frame
frame = simplegui.create_frame("Mouse selection", WIDTH, HEIGHT)
frame.set_canvas_background("White")

# register event handler
frame.set_mouseclick_handler(click)
frame.set_draw_handler(draw)

# start frame
frame.start()

例 2：

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# Examples of mouse input

import simplegui
import math

# intialize globals
width = 450
height = 300
ball_list = []
ball_radius = 15
ball_color = "Red"

# helper function
def distance(p, q):
    return math.sqrt((p[0] - q[0]) ** 2 + (p[1] - q[1]) ** 2)

# define event handler for mouse click, draw
def click(pos):
    remove = [] # 不能在下面的循环中直接删除ball_list的元素
    for ball in ball_list:
        if distance(ball, pos) < ball_radius:
            remove.append(ball)

    if remove == []:
        ball_list.append(pos)
    else:
        for ball in remove:
            ball_list.pop(ball_list.index(ball))

def draw(canvas):
    for ball in ball_list:
        canvas.draw_circle([ball[0], ball[1]], ball_radius, 1, "Black", ball_color)
    
# create frame
frame = simplegui.create_frame("Mouse selection", width, height)
frame.set_canvas_background("White")

# register event handler
frame.set_mouseclick_handler(click)
frame.set_draw_handler(draw)

# start frame
frame.start()

注意：在遍历一个 list 时，千万不要从里面删除东西，如果需要删除东西，记录下你想要删除的东西，并随后删除它们