如果你到了一定的年龄，你会记得那些被称为 DVD 播放器的古老技术设备。当不播放 DVD 时，他们会显示一个从屏幕边缘反弹回来的对角线方向的 DVD 标志。这个程序通过每次碰到边缘时改变方向来模拟这个彩色的 DVD 标志。我们还将记录一个标志点击屏幕一角的次数。这创造了一个有趣的视觉动画，特别是当一个标志与一个角完美地对齐的神奇时刻。
您不能从您的集成开发环境（IDE）或编辑器运行此程序，因为它使用了bext模块。因此，必须从命令提示符或终端运行它才能正确显示。你可以在pypi.org/project/bext找到更多关于bext模块的信息。
当你运行bouncingdvd.py时，输出将看起来像图 5-1 。
bouncingdvd.py节目的斜向移动的 DVD 标识
你可能还记得学校数学课上的笛卡尔坐标。在编程中，x 坐标表示对象的水平位置，y 坐标表示其垂直位置，就像数学中一样。然而，与数学中不同的是，原点(0, 0)在屏幕的左上角，y 坐标随着向下移动而增加。x 坐标随着对象向右移动而增加，就像数学中一样。图 5-2 显示了屏幕的坐标系统。
:原点(0,0)在屏幕的左上方，x 和 y 坐标分别向右下递增。
bext模块的goto()函数工作方式相同：调用bext.goto(0, 0)将文本光标放在终端窗口的左上角。我们使用一个 Python 字典，用关键字'color'、'direction'、'x'和'y'来表示每个跳动的 DVD 标志。'x'和'y'的值是代表窗口中徽标位置的整数。由于这些值被传递到bext.goto()，增加它们将使徽标向右和向下移动，而减少它们将使徽标向左和向上移动。
"""Bouncing DVD Logo, by Al Sweigart email@protected
A bouncing DVD logo animation. You have to be "of a certain age" to
appreciate this. Press Ctrl-C to stop.
NOTE: Do not resize the terminal window while this program is running.
This code is available at https://nostarch.com/big-book-small-python-programming
Tags: short, artistic, bext"""
import sys, random, time
try:
import bext
except ImportError:
print('This program requires the bext module, which you')
print('can install by following the instructions at')
print('https://pypi.org/project/Bext/')
sys.exit()
# Set up the constants:
WIDTH, HEIGHT = bext.size()
# We can't print to the last column on Windows without it adding a
# newline automatically, so reduce the width by one:
WIDTH -= 1
NUMBER_OF_LOGOS = 5 # (!) Try changing this to 1 or 100.
PAUSE_AMOUNT = 0.2 # (!) Try changing this to 1.0 or 0.0.
# (!) Try changing this list to fewer colors:
COLORS = ['red', 'green', 'yellow', 'blue', 'magenta', 'cyan', 'white']
UP_RIGHT = 'ur'
UP_LEFT = 'ul'
DOWN_RIGHT = 'dr'
DOWN_LEFT = 'dl'
DIRECTIONS = (UP_RIGHT, UP_LEFT, DOWN_RIGHT, DOWN_LEFT)
# Key names for logo dictionaries:
COLOR = 'color'
X = 'x'
Y = 'y'
DIR = 'direction'
def main():
bext.clear()
# Generate some logos.
logos = []
for i in range(NUMBER_OF_LOGOS):
logos.append({COLOR: random.choice(COLORS),
X: random.randint(1, WIDTH - 4),
Y: random.randint(1, HEIGHT - 4),
DIR: random.choice(DIRECTIONS)})
if logos[-1][X] % 2 == 1:
# Make sure X is even so it can hit the corner.
logos[-1][X] -= 1
cornerBounces = 0 # Count how many times a logo hits a corner.
while True: # Main program loop.
for logo in logos: # Handle each logo in the logos list.
# Erase the logo's current location:
bext.goto(logo[X], logo[Y])
print(' ', end='') # (!) Try commenting this line out.
originalDirection = logo[DIR]
# See if the logo bounces off the corners:
if logo[X] == 0 and logo[Y] == 0:
logo[DIR] = DOWN_RIGHT
cornerBounces += 1
elif logo[X] == 0 and logo[Y] == HEIGHT - 1:
logo[DIR] = UP_RIGHT
cornerBounces += 1
elif logo[X] == WIDTH - 3 and logo[Y] == 0:
logo[DIR] = DOWN_LEFT
cornerBounces += 1
elif logo[X] == WIDTH - 3 and logo[Y] == HEIGHT - 1:
logo[DIR] = UP_LEFT
cornerBounces += 1
# See if the logo bounces off the left edge:
elif logo[X] == 0 and logo[DIR] == UP_LEFT:
logo[DIR] = UP_RIGHT
elif logo[X] == 0 and logo[DIR] == DOWN_LEFT:
logo[DIR] = DOWN_RIGHT
# See if the logo bounces off the right edge:
# (WIDTH - 3 because 'DVD' has 3 letters.)
elif logo[X] == WIDTH - 3 and logo[DIR] == UP_RIGHT:
logo[DIR] = UP_LEFT
elif logo[X] == WIDTH - 3 and logo[DIR] == DOWN_RIGHT:
logo[DIR] = DOWN_LEFT
# See if the logo bounces off the top edge:
elif logo[Y] == 0 and logo[DIR] == UP_LEFT:
logo[DIR] = DOWN_LEFT
elif logo[Y] == 0 and logo[DIR] == UP_RIGHT:
logo[DIR] = DOWN_RIGHT
# See if the logo bounces off the bottom edge:
elif logo[Y] == HEIGHT - 1 and logo[DIR] == DOWN_LEFT:
logo[DIR] = UP_LEFT
elif logo[Y] == HEIGHT - 1 and logo[DIR] == DOWN_RIGHT:
logo[DIR] = UP_RIGHT
if logo[DIR] != originalDirection:
# Change color when the logo bounces:
logo[COLOR] = random.choice(COLORS)
# Move the logo. (X moves by 2 because the terminal
# characters are twice as tall as they are wide.)
if logo[DIR] == UP_RIGHT:
logo[X] += 2
logo[Y] -= 1
elif logo[DIR] == UP_LEFT:
logo[X] -= 2
logo[Y] -= 1
elif logo[DIR] == DOWN_RIGHT:
logo[X] += 2
logo[Y] += 1
elif logo[DIR] == DOWN_LEFT:
logo[X] -= 2
logo[Y] += 1
# Display number of corner bounces:
bext.goto(5, 0)
bext.fg('white')
print('Corner bounces:', cornerBounces, end='')
for logo in logos:
# Draw the logos at their new location:
bext.goto(logo[X], logo[Y])
bext.fg(logo[COLOR])
print('DVD', end='')
bext.goto(0, 0)
sys.stdout.flush() # (Required for bext-using programs.)
time.sleep(PAUSE_AMOUNT)
# If this program was run (instead of imported), run the game:
if __name__ == '__main__':
try:
main()
except KeyboardInterrupt:
print()
print('Bouncing DVD Logo, by Al Sweigart')
sys.exit() # When Ctrl-C is pressed, end the program. 在输入源代码并运行几次之后，尝试对其进行实验性的修改。标有(!)的注释对你可以做的小改变有建议。你也可以自己想办法做到以下几点：
- 更改
NUMBER_OF_LOGOS以增加屏幕上跳跃标志的数量。 - 更改
PAUSE_AMOUNT以加快或减慢徽标的速度。
试着找出下列问题的答案。尝试对代码进行一些修改，然后重新运行程序，看看这些修改有什么影响。
- 如果把第 20 行的
WIDTH, HEIGHT = bext.size()改成WIDTH, HEIGHT = 10, 5会怎么样？ - 如果把第 52 行的
DIR: random.choice(DIRECTIONS)换成DIR: DOWN_RIGHT会怎么样？ - 如何让
'Corner bounces:'文字不出现在屏幕上？ - 如果删除或注释掉第 57 行的
cornerBounces = 0,会得到什么错误信息？