Python学习笔记(8)class, for loop, while loop, spaceship project

1 class中的函数

1.1 __init__()是类的初始化函数

1.2 __str__()是类用来转化为string的函数。这样 print 打印类对象的时候，就可以正确打印了。

1.3 eg 生成一团随机点集的例子

# Particle class example used to simulate diffusion of molecules

import simplegui
import random

# global constants
WIDTH = 600
HEIGHT = 400
PARTICLE_RADIUS = 5
COLOR_LIST = ["Red", "Green", "Blue", "White"]
DIRECTION_LIST = [[1,0], [0, 1], [-1, 0], [0, -1]]

# definition of Particle class
class Particle:
    
    # initializer for particles
    def __init__(self, position, color):
        self.position = position
        self.color = color
        
    # method that updates position of a particle    
    def move(self, offset):
        self.position[0] += offset[0]
        self.position[1] += offset[1]
        
    # draw method for particles
    def draw(self, canvas):
        canvas.draw_circle(self.position, PARTICLE_RADIUS, 1, self.color, self.color)
    
    # string method for particles
    def __str__(self):
        return "Particle with position = " + str(self.position) + " and color = " + self.color

# draw handler
def draw(canvas):
    for p in particle_list:
        p.move(random.choice(DIRECTION_LIST))
    
    for p in particle_list:
        p.draw(canvas)

# create frame and register draw handler
frame = simplegui.create_frame("Particle simulator", WIDTH, HEIGHT)
frame.set_draw_handler(draw)

# create a list of particles
particle_list = []
for i in range(100):
    p = Particle([WIDTH / 2, HEIGHT / 2], random.choice(COLOR_LIST))
    particle_list.append(p)

# start frame
frame.start()

2 while loop and for loop

2.1 demo

def list_extend_many1(lists):
    """Returns a list that is the concatenation of all the lists in the given list-of-lists."""
    result = []
    for l in lists:
        result.extend(l)
    return result

def list_extend_many2(lists):
    result = []
    i = 0
    while i < len(lists): 
        result.extend(lists[i])
        i += 1
    return result

def list_extend_many3(lists):
    result = []
    i = 0
    while i < len(lists): 
        result += lists[i]
        i += 1
    return result

def list_extend_many4(lists):
    result = []
    while len(lists) > 0:
        result.extend(lists.pop(0))
    return result

def list_extend_many5(lists):
    result = []
    i = len(lists) # i=4
    while i >= 0:
        i -= 1
        result.extend(lists[i])
    return result

2.2

list: an ordered sequence

dictionary: key-value mappings

sets: unordered collection of data with no duplicate

3 sets例子

3.1 sets例子 http://www.codeskulptor.org/#examples-sets.py

ordered of the elements in sets is not guaranteed.

instructors = set(['Rixner', 'Warren', 'Greiner', 'Wong’]) //使用了set()函数来建立一组set，输入参数为一个list. 这里的list=['Rixner', 'Warren', 'Greiner', 'Wong’]

instructors = set([]) //使用了set()来建立一组set，参数为一个list，这里的list=NULL

3 spaceship project

3.1 animated sprites demo

http://www.codeskulptor.org/#examples-asteroid_animation.py