import turtle
width=30
num=18
x1=[(-400,400),(-400+width*num,400)]
y1=[(-400,400),(-400,400-width*num)]
t=turtle.Pen() #调出画笔
t.speed(10)
for i in range(num+1):
t.penup()
t.goto(x1[0][0],x1[0][1]-30*i)
t.pendown()
t.goto(x1[1][0],x1[1][1]-30*i)
for i in range(num+1):
t.penup()
t.goto(y1[0][0]+30*i,y1[0][1])
t.pendown()
t.goto(y1[1][0]+30*i,y1[1][1])
turtle.done()
老师,你好,我对这整个代码都不是很了解,能麻烦讲解下吗