drawing a line moves like a clock pointer in pygame - pygame

Question

I am trying to draw a line moving in the same way as a clock pointer , but when i run the program the line move like 20 degrees then the program got frozen , and i can read that :"ValueError: math domain error"
here is the code i have written :
import pygame
import sys
import time
import math
from pygame.locals import *
pygame.init()
windowSurface = pygame.display.set_mode((300, 600), 0, 32)
pygame.display.set_caption("circle_line")
BLACK = (0, 0, 0)
WHITE = (250, 250, 250)
R = 50
CIRCLE_LINE_START_X = 150
CIRCLE_LINE_START_Y = 300
CIRCLE_LINE_END_X = CIRCLE_LINE_START_X
CIRCLE_LINE_END_Y = CIRCLE_LINE_START_Y - R
MOVE_SPEED = 3
while True:
for event in pygame.event.get():
if event.type == QUIT:
pygame.quit()
sys.exit()
if CIRCLE_LINE_END_X <= CIRCLE_LINE_START_X and CIRCLE_LINE_END_Y <= CIRCLE_LINE_START_Y :
CIRCLE_LINE_END_X -= MOVE_SPEED
CIRCLE_LINE_END_Y = math.sqrt(R**2 - ((CIRCLE_LINE_END_X - CIRCLE_LINE_START_X)**2)) + CIRCLE_LINE_START_Y
if CIRCLE_LINE_END_X <= CIRCLE_LINE_START_X and CIRCLE_LINE_END_Y >= CIRCLE_LINE_START_Y :
CIRCLE_LINE_END_X += MOVE_SPEED
CIRCLE_LINE_END_Y = math.sqrt(R**2 - ((CIRCLE_LINE_END_X - CIRCLE_LINE_START_X)**2)) + CIRCLE_LINE_START_Y
if CIRCLE_LINE_END_X >= CIRCLE_LINE_START_X and CIRCLE_LINE_END_Y >= CIRCLE_LINE_START_Y :
CIRCLE_LINE_END_X += MOVE_SPEED
CIRCLE_LINE_END_Y = math.sqrt(R**2 - ((CIRCLE_LINE_END_X - CIRCLE_LINE_START_X)**2)) + CIRCLE_LINE_START_Y
if CIRCLE_LINE_END_X >= CIRCLE_LINE_START_X and CIRCLE_LINE_END_Y <= CIRCLE_LINE_START_Y :
CIRCLE_LINE_END_X -= MOVE_SPEED
CIRCLE_LINE_END_Y = math.sqrt(R**2 - ((CIRCLE_LINE_END_X - CIRCLE_LINE_START_X)**2)) + CIRCLE_LINE_START_Y
windowSurface.fill(WHITE)
pygame.draw.line(windowSurface, BLACK, (CIRCLE_LINE_START_X, CIRCLE_LINE_START_Y), (CIRCLE_LINE_END_X, CIRCLE_LINE_END_Y), 3)
pygame.display.update()
time.sleep(0.02)
any help to find out my mistake will be appreciated.
thank you.

Answer 1

This error is because you are trying to calculate the square root of a negative number, concretely the result of R**2 - ((CIRCLE_LINE_END_X - CIRCLE_LINE_START_X)**2).
However, if you want to draw something based on a circular movement, I suggest you to use a variable called DEGREES and increment it in each iteration. Then you can use math.sin and math.cos to calculate the distance based on the angle.

Answer 2

i made some modulations in the algorithm i had used , and this code is giving acceptable result comparing with the code above , here is the code for who is interesting:
import pygame
import sys
import time
import math
from pygame.locals import *
pygame.init()
windowSurface = pygame.display.set_mode((300, 600), 0, 32)
pygame.display.set_caption("circle_line")
BLACK = (0, 0, 0)
WHITE = (250, 250, 250)
R = 50
CIRCLE_LINE_START_X = 150
CIRCLE_LINE_START_Y = 300
MIN_X = CIRCLE_LINE_START_X - R
MAX_X = CIRCLE_LINE_START_X + R
CIRCLE_LINE_END_X = MIN_X
CIRCLE_LINE_END_Y = math.sqrt(R**2 - ((CIRCLE_LINE_END_X - CIRCLE_LINE_START_X)**2)) + CIRCLE_LINE_START_Y
MOVE_SPEED = 5 # has to be a number where as ( R % MOVE_SPEED = 0 )
DIRECTION = "right"
while True:
for event in pygame.event.get():
if event.type == QUIT:
pygame.quit()
sys.exit()
if CIRCLE_LINE_END_X >= MAX_X :
CIRCLE_LINE_END_X = MAX_X
DIRECTION = "left"
if CIRCLE_LINE_END_X <= MIN_X :
CIRCLE_LINE_END_X = MIN_X
DIRECTION = "right"
if DIRECTION == "right":
CIRCLE_LINE_END_X += MOVE_SPEED
CIRCLE_LINE_END_Y = math.sqrt(R**2 - ((CIRCLE_LINE_END_X - CIRCLE_LINE_START_X)**2)) + CIRCLE_LINE_START_Y
if DIRECTION == "left":
CIRCLE_LINE_END_X -= MOVE_SPEED
CIRCLE_LINE_END_Y = CIRCLE_LINE_START_Y - math.sqrt(R**2 - ((CIRCLE_LINE_END_X - CIRCLE_LINE_START_X)**2))
windowSurface.fill(WHITE)
pygame.draw.line(windowSurface, BLACK, (CIRCLE_LINE_START_X, CIRCLE_LINE_START_Y), (CIRCLE_LINE_END_X, CIRCLE_LINE_END_Y), 3)
pygame.display.update()
time.sleep(0.02)