构建自己的循环

内建函数range(n):构建一个0到n-1的整数数字列表

class range(stop)

class range(start, stop[, step])

内建函数list():构建列表

for语句：

for_stmt ::=  "for" target_list "in" expression_list ":" suite
              ["else" ":" suite]

用for循环生成四个花瓣

# Rosette4.py
import turtle
t = turtle.Pen()
for x in range(4):
    t.circle(100)
    t.left(90)

用for循环生成六个花瓣

# Rosette6.py
import turtle
t = turtle.Pen()
for x in range(6):
    t.circle(100)
    t.left(60)

增加用户输入功能

获取输入的数字字符串：turtle.numinput(title, prompt, default=None, minval=None, maxval=None)

# RosetteGoneWild.py
import turtle
t = turtle.Pen()
# Ask the user for the number of circles in their rosette, default to 6
number_of_circles = int(turtle.numinput("Number of circles",
                                        "How many circles in your rosette?", 6))
for x in range(number_of_circles):
    t.circle(100)
    t.left(360/number_of_circles)

游戏循环和while循环

while语句：适合循环次数不确定的情况

while_stmt ::=  "while" assignment_expression ":" suite
                ["else" ":" suite]

# SayOurNames.py - lets everybody print their name on the screen
# Ask the user for their name
name = input("What is your name? ")
# Keep printing names until we want to quit
while name != "":
    # Print their name 100 times
    for x in range(100):
        # Print their name followed by a space, not a new line
        print(name, end = " ")
    print()   # After the for loop, skip down to the next line
    # Ask for another name, or quit
    name = input("Type another name, or just hit [ENTER] to quit: ")
print("Thanks for playing!")

家庭成员螺旋线

# SpiralFamily.py - prints a colorful spiral of names
import turtle     # Set up turtle graphics
t = turtle.Pen()  
turtle.bgcolor("black")
colors = ["red", "yellow", "blue", "green", "orange",
        "purple", "white", "brown", "gray", "pink" ]
family = []       # Set up an empty list for family names
# Ask for the first name
name = turtle.textinput("My family",
                        "Enter a name, or just hit [ENTER] to end:")
# Keep asking for names
while name != "":
    # Add their name to the family list
    family.append(name)
    # Ask for another name, or end
    name = turtle.textinput("My family",
                        "Enter a name, or just hit [ENTER] to end:")
# Draw a spiral of the names on the screen
for x in range(100):
    t.pencolor(colors[x%len(family)]) # Rotate through the colors
    t.penup()                         # Don't draw the regular spiral lines
    t.forward(x*4)                    # Just move the turtle on the screen
    t.pendown()                       # Draw the next family member's name
    t.write(family[x%len(family)], font = ("Arial", int((x+4)/4), "bold") )
    t.left(360/len(family) + 2)         # Turn left for our spiral

整合-病毒式的螺旋线

# ViralSpiral.py - a spiral of spirals!
import turtle
t = turtle.Pen()
t.penup()
turtle.bgcolor("black")
# Ask the user for the number of sides, default to 4, min 2, max 6
sides = int(turtle.numinput("Number of sides",
            "How many sides in your spiral of spirals? (2-6)", 4,2,6))
colors = ["red", "yellow", "blue", "green", "purple", "orange"]
# Our outer spiral loop
for m in range(100):
    t.forward(m*4)
    position = t.position() # Remember this corner of the spiral
    heading = t.heading()   # Remember the direction we were heading
    print(position, heading)
    # Our "inner" spiral loop
    # Draws a little spiral at each corner of the big spiral
    for n in range(int(m/2)):
        t.pendown()
        t.pencolor(colors[n%sides])
        t.forward(2*n)
        t.right(360/sides - 2)
        t.penup()
    t.setx(position[0])     # Go back to the big spiral's x location
    t.sety(position[1])     # Go back to the big spiral's y location
    t.setheading(heading)   # Point in the big spiral's heading
    t.left(360/sides + 2)   # Aim at the next point on the big spiral

编程挑战

螺旋线玫瑰花瓣

修改病毒式的螺旋线程序，将小的螺旋线替换为玫瑰花瓣，运行结果如下图

4-循环很有趣