turtle.Screen().screensize() not outputting the right screensize

Question

I have written some code to place dots all around the screen randomly; however, it does not cover the entire screen:

import turtle
import random

t = turtle.Turtle()

color = ["red", "green", "blue", "pink", "yellow", "purple"]
t.speed(-1)
for i in range(0, 500):
    print(turtle.Screen().screensize())
    z = turtle.Screen().screensize()
    x = z[0]
    y = z[1]
    t.color(color[random.randint(0,5)])
    t.dot(4)
    t.setposition(random.randint(-x,x), random.randint(-y,y))


turtle.done()

output

Answer 1

"Screen" refers to the turtle's logical boundaries (scrollable area) which may not be the same as the window size.

Call Screen().setup(width, height) to set your window size, then use the Screen().window_width() and Screen().window_height() functions to access its size.

You could also make sure the screensize matches the window size, then use it as you are doing. Set the screen size with Screen().screensize(width, height).

Additionally, your random number selection is out of bounds. Use

random.randint(0, width) - width // 2

to shift the range to be centered on 0.

Putting it together:

from random import choice, randint
from turtle import Screen, Turtle


screen = Screen()
screen.setup(480, 320)
colors = "red", "green", "blue", "pink", "yellow", "purple",
t = Turtle()
t.speed("fastest")

for _ in range(0, 100):
    t.color(choice(colors))
    t.dot(4)
    w = screen.window_width()
    h = screen.window_height()
    t.setposition(randint(0, w) - w // 2, randint(0, h) - h // 2)

screen.exitonclick()