screen.update returning an error (Python Turtle module)

Question

In my snake code project, I need to set the tracer to 0 and then use the update method to render a snake game like animation for my turtles. Here is my code:

# setup screen

screen = Screen()
screen.setup(width=600, height=600)
screen.bgcolor("black")
screen.title("Welcome to the snake game!")
screen.tracer(0)

# create a snake body, aka three white turtles

starting_pos = [(0,0), (-20,0), (-40,0)]

segments = []

for position in starting_pos:

    new_seg = Turtle("square")
    new_seg.color("white")
    new_seg.penup()
    new_seg.goto(position)

    segments.append(new_seg)

# move the snake

game_is_on = True

while game_is_on:
    screen.update()
    time.sleep(0.1)

for seg_num in range(len(segments) - 1, 0, -1):

    new_x = segments[seg_num - 1].xcor
    new_y = segments[seg_num - 1].ycor
    segments[seg_num].goto(new_x, new_y)

Here is the error it gives:

TypeError: unsupported operand type(s) for +: 'method' and 'float'

What should I do?

cdlane · Accepted Answer · 2022-05-19 15:35:16Z

Your immediate problem is these two lines:

new_x = segments[seg_num - 1].xcor
new_y = segments[seg_num - 1].ycor

xcor and ycor are methods, not properties and so should be invoked:

new_x = segments[seg_num - 1].xcor()
new_y = segments[seg_num - 1].ycor()

However, this fix alone won't get your snake moving, the segments will just pile up on each other. You also need to move the head forward. Below is my rework of your code that tosses while True: which has no place in an event-driven world like turtle:

from turtle import Screen, Turtle

screen = Screen()
screen.setup(width=600, height=600)
screen.title("Welcome to the snake game!")
screen.bgcolor('black')
screen.tracer(0)

# create a snake body, aka three white turtles

starting_pos = [(0, 0), (-20, 0), (-40, 0)]

segments = []

for position in starting_pos:
    segment = Turtle('square')
    segment.color('white')
    segment.penup()
    segment.goto(position)

    segments.append(segment)

# move the snake

game_is_on = True

def move():
    if game_is_on:
        for seg_num in range(len(segments) - 1, 0, -1):
            new_position = segments[seg_num - 1].position()
            segments[seg_num].goto(new_position)

        segments[0].forward(20)

        screen.update()
        screen.ontimer(move, 100)  # milliseconds

move()

screen.mainloop()

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