Styjun

I am trying to draw a red Stop sign, outlined in white. However, I can't seem to figure out why the red octagon is not filling in.

If the octagon is still open, would that be why it's not filling? If it is, how can I check to see if it's open?

import turtle
turtle.bgcolor("black")
turtle.penup()
turtle.goto(-104,-229)
# Draws white octagon outline
for i in range(8):
 turtle.pensize(10)
 turtle.color("white") 
 turtle.pendown()
 turtle.forward(193)
 turtle.right(5)
 turtle.left(50)

# Draws red octagon
turtle.penup()
turtle.goto(-100,-220)
for i in range(8):
 turtle.pensize(10)
 turtle.color("red")
 turtle.fillcolor("red")
 turtle.begin_fill() 
 turtle.pendown()
 turtle.forward(185)
 turtle.right(5)
 turtle.left(50)
 turtle.end_fill()

# Writes "STOP"
turtle.penup() 
turtle.goto(5,-50)
turtle.setheading(360 / 8 / 2)
turtle.pendown()
turtle.stamp() 
turtle.pencolor("white")
turtle.shapesize(0.9)
turtle.stamp()
turtle.shapesize(1.0)
turtle.write("STOP", align="center", font=("Arial",110,"normal")) 
turtle.done()

You need to put the begin and end fill outside the loop as it would be just filling one line at a time

# Draws red octagon
turtle.penup()
turtle.goto(-100,-220)
turtle.pensize(10)
turtle.color("red")
turtle.fillcolor("red")
turtle.begin_fill()
for i in range(8):
 turtle.pendown()
 turtle.forward(185)
 turtle.right(5)
 turtle.left(50)
turtle.end_fill()

I see two issues with your code. First, you put the begin_fill() and end_fill() inside your octogon loop -- they should wrap around the outside of the loop, not be part of it. Second, you've generally made things more complicated than necessary including throwing in code that has no bearing on your result (e.g stamp(), shapesize(), setheading(), etc.). Here's simplfied rework of your code with the fill fixed:

from turtle import Screen, Turtle

SIDE = 200
PEN_SIZE = 10
FONT_SIZE = 150
FONT = ("Arial", FONT_SIZE, "bold")

screen = Screen()
screen.bgcolor("black")

turtle = Turtle()
turtle.hideturtle()
turtle.pensize(PEN_SIZE)
turtle.penup()

# Draw white octagon with red fill
turtle.goto(-SIDE/2, -SIDE/2 + -SIDE/(2 ** 0.5)) # octogon geometry
turtle.color("white", "red") # color() sets both pen and fill colors
turtle.pendown()

turtle.begin_fill()
for _ in range(8):
 turtle.forward(SIDE)
 turtle.left(45)
turtle.end_fill()

turtle.penup()

# Write "STOP"
turtle.goto(0, -FONT_SIZE/2) # roughly font baseline
turtle.pencolor("white")

turtle.write("STOP", align="center", font=FONT) # write() doesn't need pendown()

screen.exitonclick()