這幾天開始學Python了，為加深印象，我把學過的怕忘的知識整理記錄下來。
學習Python用的教材是《Python語言程序設計（英文版）》。
練習代碼用的編譯器是Python3.5（64-bit）。
第一條語句：
print("Welcome to Python")
Python的句尾都是沒有標點符號(punctuation)的。
此外，Python是一門格外注意縮進的語言。在體內的句子可以用tab和space來進行縮進，但要按照一定的規則，否則就會報錯。
目前我遇到的有關縮進的報錯有這幾種：
1. TabError: inconsistent use of tabs and spaces in indentation
錯誤原因：tab和space混用不當，造成縮進問題。我試了一下，貌似用體內用tab縮進后再用space縮進不會報錯，但若先用space再用tab則可能造成該錯誤。
2. SyntaxError: invalid syntax
錯誤原因：語法錯誤，一行的最前方如果是...表明還在體內，此時若要寫體外語句，則需要按下回車，最前方為>>>時則可以另起一體。
3. IndentationError: unexpected indent
錯誤原因：不需要縮進時縮進
4. IndentationError: expected an indented block
錯誤原因：該縮進時沒縮進
turtle()
turtle.write("turtle is very interesting") #turtle writes down "turtle is very interesting" from the present position
turtle.forward(100) #turtle goes forward 100 pixels in its present direction
turtle.color("red") #the line turtle draws becomes red
turtle.right(90)
turtle.left(45) #turtle turns right 90 degrees or turns left 45 degrees
turtle.penup() # turtle moves without track
turtle.goto(50,100) #the primitive position of turtle is (0,0), and 50 is the xcor of turtle and 100 is the ycor of turtle
turtle.pendown() #turtle returns to the paper and will move with track
turtle.done() #
turtle.pensize(3) # assign the size of line
turtle.begin_fill()
...
turtle.end_fill() # the closed graph between begin_fill() and end_fill() will be filled with the color of turtle
turtle.circle(50) #turtle draws a circle with radius 50.
turtle.circle(50,steps=3) # draws a closed graph with 3 equivalent?edges. When the steps become bigger, the graph resembles circle more.
turtle.speed(10) # the drawing speed ranging 1-10, 10 is the fastest,?and 1 is the slowest
turtle.undo()
turtle.screensize(w,h) # w is width and h is height of the screen
turtle.clear() # clear the screen content but don't change the position and status of turtle
turtle.reset() # clear the screen content and reset turtle to the initiative status
input &?output:
variable = input("please input a number") #variable is a string
variable1 = eval(input("please input a number")) # variable1 is a number
variable2 = eval(variable)
>>>print(input("please input a number")) #assume input number 8
'8'
>>>print(eval(input("please input a number"))) #assume input number 8
8
print("The float average of ",variable1," and ",variable2," is ",(variable1+variable2)/2)
print("The integer?average of ",variable1," and ",variable2," is ",(variable1+variable2)//2)
>>>print("AAA",end='&&&')
AAA&&&
Exchange:
x,y=y,x # Fantastic! Thanks to the highly encapsulation?of Python we can easily exchange the value of two variables.
Time:
import time
currentTime=time.time()
ord and chr function:
ch='a'
>>>ord(ch)
97
>>>chr(98)
'b'
Random()
import random
random.random() # generate a random float ranging [0,1)
random.randint(a,b) # generate an integer ranging [a,b]
random.randrange(a,b) # generate an integer ranging [a,b)
If:
if boolean-expression:
?statement
elif boolean-expression:
?statement
else:
?statement
貓和老鼠游戲：
import time
import turtle
boxsize=200
caught=False
score=0
window=turtle.Screen()
mouse=turtle.Turtle()
cat=turtle.Turtle()
def checkbound():
?global boxsize
?if mouse.xcor()>boxsize:
? mouse.goto(boxsize,mouse.ycor())
?if mouse.xcor()<-boxsize:
? mouse.goto(-boxsize,mouse.ycor())
?if mouse.ycor()>boxsize:
? mouse.goto(mouse.xcor(),boxsize)
?if mouse.ycor<-boxsize:
? mouse.goto(mouse.xcor(),-boxsize)
def up():
?mouse.forward(10)
?checkbound()
def left():
?mouse.left(45)
def right():
?mouse.right(45)
def back():
?mouse.backward(10)
?checkbound()
def quitTurtle():
?window.bye()
mouse.penup()
mouse.goto(100,100)
window.onkeypress(up,"Up")
window.onkeypress(left,"Left")
window.onkeypress(right,"Right")
window.onkeypress(back,"Down")
window.onkeypress(quitTurtle,"Escape")
difficulty=window.numinput("難度","請輸入游戲的難度（1~5）")
window.listen()
while not caught:
?cat.setheading(cat.towards(mouse))
?cat.forward(8+difficulty)
?score+=1
?if cat.distance(mouse)<5:
? caught=True
? time.sleep(0.2-(0.01*difficulty))
window.textinput("Game Over","游戲得分："+str(score*difficulty))
window.bye()
