Python学习笔记(6)ListandKeyboardControl

下面的笔记内容来自coursera上的Python公开课。

List注意1 List中的value类型可以不一致
list_test=['abc',1.3,4,[4,5,6]] print list_test         #['abc', 1.3, 4, [4, 5, 6]]

List注意2 list分为两半list
If we want to split a list my_list into two halves, which of the following uses slices to do so correctly? More precisely, if the length of my_list is 2n, i.e., even, then the two parts should each have length n. If its length is 2n+1, i.e., odd, then the two parts should have lengths n and n+1. my_list[: len(my_list) // 2] and my_list[len(my_list) // 2 :] my_list[0 : len(my_list) // 2] and my_list[len(my_list) // 2 : len(my_list)]

List注意3 看下面几个列子，理解list是否是global variable

###################################
# Mutation vs. assignment


################
# Look alike, but different

a = [4, 5, 6]
b = [4, 5, 6]
print "Original a and b:", a, b
print "Are they same thing?", a is b

a[1] = 20
print "New a and b:", a, b
print

################
# Aliased

c = [4, 5, 6]
d = c
print "Original c and d:", c, d
print "Are they same thing?", c is d

c[1] = 20
print "New c and d:", c, d
print

################
# Copied

e = [4, 5, 6]
f = list(e)
print "Original e and f:", e, f
print "Are they same thing?", e is f

e[1] = 20
print "New e and f:", e, f
print


###################################
# Interaction with globals


a = [4, 5, 6]

def mutate_part(x):
    a[1] = x

def assign_whole(x):
    a = x

def assign_whole_global(x):
    global a
    a = x

mutate_part(100)
print a

assign_whole(200)
print a

assign_whole_global(300)
print a

Original a and b: [4, 5, 6] [4, 5, 6]
Are they same thing? False
New a and b: [4, 20, 6] [4, 5, 6]

Original c and d: [4, 5, 6] [4, 5, 6]
Are they same thing? True
New c and d: [4, 20, 6] [4, 20, 6]

Original e and f: [4, 5, 6] [4, 5, 6]
Are they same thing? False
New e and f: [4, 20, 6] [4, 5, 6]

[4, 100, 6]
[4, 100, 6]
300

###################################
# Lists (mutable) vs. tuples (immutable)

print [4, 5, 6]

print (4, 5, 6)

print type([4, 5, 6])

print type((4, 5, 6))

a = [4, 5, 6]
a[1] = 100
print a

b = (4, 5, 6)
b[1] = 100  #Line 17: TypeError: 'tuple' does not support item assignment
print b

KeyboardControl例1 Keyboard echo

import simplegui

# initialize state
current_key = ' '

# event handlers
def keydown(key):
    global current_key
    current_key = chr(key)
   
def keyup(key):
    global current_key
    current_key = ' '
   
def draw(c):
    # NOTE draw_text now throws an error on some non-printable characters
    # Since keydown event key codes do not all map directly to
    # the printable character via ord(), this example now restricts
    # keys to alphanumerics
   
    if current_key in "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789":
        c.draw_text(current_key, [10, 25], 20, "Red")   
       
# create frame            
f = simplegui.create_frame("Echo", 35, 35)

# register event handlers
f.set_keydown_handler(keydown)
f.set_keyup_handler(keyup)
f.set_draw_handler(draw)

# start frame
f.start()

# control the position of a ball using the arrow keys

import simplegui

# Initialize globals
WIDTH = 600
HEIGHT = 400
BALL_RADIUS = 20

ball_pos = [WIDTH / 2, HEIGHT / 2]

# define event handlers
def draw(canvas):
    canvas.draw_circle(ball_pos, BALL_RADIUS, 2, "Red", "White")

def keydown(key):
    vel = 4
    if key == simplegui.KEY_MAP["left"]:
        ball_pos[0] -= vel
    elif key == simplegui.KEY_MAP["right"]:
        ball_pos[0] += vel
    elif key == simplegui.KEY_MAP["down"]:
        ball_pos[1] += vel
    elif key == simplegui.KEY_MAP["up"]:
        ball_pos[1] -= vel        
    
# create frame 
frame = simplegui.create_frame("Positional ball control", WIDTH, HEIGHT)

# register event handlers
frame.set_draw_handler(draw)
frame.set_keydown_handler(keydown)

# start frame
frame.start()

# Ball motion with an explicit timer

import simplegui

# Initialize globals
WIDTH = 600
HEIGHT = 400
BALL_RADIUS = 20

init_pos = [WIDTH / 2, HEIGHT / 2]
vel = [0, 3]  # pixels per tick
time = 0

# define event handlers
def tick():
    global time
    time = time + 1

def draw(canvas):
    # create a list to hold ball position
    ball_pos = [0, 0]

    # calculate ball position
    ball_pos[0] = init_pos[0] + time * vel[0]
    ball_pos[1] = init_pos[1] + time * vel[1]
    
    # draw ball
    canvas.draw_circle(ball_pos, BALL_RADIUS, 2, "Red", "White")

# create frame
frame = simplegui.create_frame("Motion", WIDTH, HEIGHT)

# register event handlers
frame.set_draw_handler(draw)

timer = simplegui.create_timer(100, tick)

# start frame
frame.start()
timer.start()

1 If you want to simply access a global variable you just use its name. However to change its value you need to use the global keyword.
2 问题 draw()里的ball_pos明明不是global variable，为什么update表现和global variable的update表现是一样的呢？因为在函数中对变量如果进行mutation，则把此变量看做global variable;如果进行assign且声明此变量为global,则把此变量看做global variable;如果进行assign并且不声明此变量为global,把此变量看做local variable.

# Ball motion with an implicit timer

import simplegui

# Initialize globals
WIDTH = 600
HEIGHT = 400
BALL_RADIUS = 20

ball_pos = [WIDTH / 2, HEIGHT / 2]
vel = [0, 1] # pixels per update (1/60 seconds)

# define event handlers
def draw(canvas):
    # Update ball position
    ball_pos[0] += vel[0]
    ball_pos[1] += vel[1]

    # Draw ball
    canvas.draw_circle(ball_pos, BALL_RADIUS, 2, "Red", "White")

# create frame
frame = simplegui.create_frame("Motion", WIDTH, HEIGHT)

# register event handlers
frame.set_draw_handler(draw)

# start frame
frame.start()

import simplegui

# Initialize globals
WIDTH = 600
HEIGHT = 400
BALL_RADIUS = 20

ball_pos = [WIDTH / 2, HEIGHT / 2]
vel = [-40.0 / 60.0,  5.0 / 60.0]

# define event handlers
def draw(canvas):
    # Update ball position
    ball_pos[0] += vel[0]
    ball_pos[1] += vel[1]
    
    # collide and reflect off of left hand side of canvas
    if ball_pos[0] <= BALL_RADIUS:
        vel[0] = - vel[0]

    
    # Draw ball
    canvas.draw_circle(ball_pos, BALL_RADIUS, 2, "Red", "White")

# create frame
frame = simplegui.create_frame("Ball physics", WIDTH, HEIGHT)

# register event handlers
frame.set_draw_handler(draw)

# start frame
frame.start()

例子6 从position和velocity入手改变小球移动

# control the velocity of a ball using the arrow keys

import simplegui

# Initialize globals
WIDTH = 600
HEIGHT = 400
BALL_RADIUS = 20

ball_pos = [WIDTH / 2, HEIGHT / 2]
vel = [0, 0]

# define event handlers
def draw(canvas):
    # Update ball position
    ball_pos[0] += vel[0]
    ball_pos[1] += vel[1]

    # Draw ball
    canvas.draw_circle(ball_pos, BALL_RADIUS, 2, "Red", "White")

def keydown(key):
    acc = 1
    if key==simplegui.KEY_MAP["left"]:
        vel[0] -= acc
    elif key==simplegui.KEY_MAP["right"]:
        vel[0] += acc
    elif key==simplegui.KEY_MAP["down"]:
        vel[1] += acc
    elif key==simplegui.KEY_MAP["up"]:
        vel[1] -= acc
        
    print ball_pos
    
# create frame 
frame = simplegui.create_frame("Velocity ball control", WIDTH, HEIGHT)

# register event handlers
frame.set_draw_handler(draw)
frame.set_keydown_handler(keydown)

# start frame
frame.start()