Python龟箭头没有面向正确的方向

Question

I'm trying to draw an arrow using Python turtle. But when it gets to the head of the arrow, I get the turtle heading and add 45 degrees to draw half of the arrow, then get back to the same position to draw the other part. I set the correct angle but then everything goes wrong:

Initialization

StartPointX=0
StartPointY=0
MaxX=100
MaxY=100

Drawing The arrow line

Brush.goto(StartPointX,StartPointY)
Brush.goto(MaxX,MaxY)

Drawing arrow head

Brush.left(45)
Brush.backward(20)
Brush.forward(20)
Brush.right(90)
Brush.backward(20)

Output image:

Answer 1

The problem is you're ignoring the heading of the turtle. When you use goto() the heading of the turtle is unchanged. When you write left(45) , it's left 45 degrees relative to what? Left of the current heading, which hasn't been set:

from turtle import Screen, Turtle

StartPointX = 0
StartPointY = 0
MaxX = 100
MaxY = 100

screen = Screen()
brush = Turtle()

# Drawing The arrow line

brush.penup()
brush.goto(StartPointX, StartPointY)
brush.pendown()

brush.setheading(brush.towards(MaxX, MaxY))
brush.goto(MaxX, MaxY)

# Drawing arrow head

brush.left(45)
brush.backward(20)
brush.forward(20)
brush.right(90)
brush.backward(20)

brush.hideturtle()
screen.exitonclick()

Another way to approach this:

MaxX = 100
MaxY = 100

# ...

brush.setheading(brush.towards(MaxX, MaxY))
brush.goto(MaxX, MaxY)

Is to control the heading and use forward() instead of goto() :

Distance = 140

# ...

brush.setheading(45)
brush.forward(Distance)