Your code doesn't run as posted so let's rework it into a complete solution incorporating @oglox's undraw()
suggestion:
import math
import graphics
win = graphics.GraphWin(width=500, height=500)
win.setCoords(-250, -250, 250, 250)
win.setBackground("yellow")
CENTER = graphics.Point(0, 0)
RADIUS = 150
line = None
for theta in range(360):
angle = math.radians(theta)
x = RADIUS * math.cos(angle)
y = RADIUS * math.sin(angle)
point = graphics.Point(x, y)
if line: # None is False in a boolean context
line.undraw()
line = graphics.Line(CENTER, point)
line.draw(win)
win.close()
This presents a somewhat wispy, flickering line. We can do slightly better by drawing and undrawing in the reverse order:
old_line = None
for theta in range(360):
angle = math.radians(theta)
x = RADIUS * math.cos(angle)
y = RADIUS * math.sin(angle)
point = graphics.Point(x, y)
new_line = graphics.Line(CENTER, point)
new_line.draw(win)
if old_line: # None is False in a boolean context
old_line.undraw()
old_line = new_line
This gives a thicker looking line and slightly less flicker.