How to remove the straight line from this sine wave

Question

How can I remove the line that runs through the middle of this sine wave?

import pygame, sys, math
from pygame.locals import *

pygame.init()
clock = pygame.time.Clock()

points = []

screen = pygame.display.set_mode((500, 500))

while True:
    clock.tick(60)
    screen.fill((0, 0, 0))

    # Draw Sine Wave
    for i in range(500):
        n = int(math.sin(i / 500 * 4 * math.pi) * 50 + 240)
        points.append([i, n])

    pygame.draw.lines(screen, (0, 255, 55), False, points, 2)

    # Events
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            pygame.quit()
            sys.exit()

        if event.type == KEYDOWN:
            if event.key == K_ESCAPE:
                pygame.quit()
                sys.exit()
    pygame.display.update()

Answer 1

You have two mistakes

1. Use False instead of True to draw open polygon

    pygame.draw.lines(screen, (0, 255, 55), False, points, 2)
   

2. In every loop you add new points to list and then after last point (499,0) you have (0,0) which create vertical line from right to left. You can see it if you use print(len(point)) - you will get values 500,1000,1500,etc. You should clear points in every loop. Or you should generate points only once - before while loop.

---

Clear points before creating new list - it can be useful if you want animated wave.

while True:
    clock.tick(60)
    screen.fill((0, 0, 0))

    points = []  # <--- clear it

    # Draw Sine Wave
    for i in range(500):
        n = int(math.sin(i / 500 * 4 * math.pi) * 50 + 240)
        points.append([i, n])

    pygame.draw.lines(screen, (0, 255, 55), False, points, 1)

    # Events
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            pygame.quit()
            sys.exit()

        if event.type == KEYDOWN:
            if event.key == K_ESCAPE:
                pygame.quit()
                sys.exit()
    pygame.display.update()

Or generate it before loop - if you want static wave

# generate it only once - before `while` loop

points = []

# Draw Sine Wave
for i in range(500):
    n = int(math.sin(i / 500 * 4 * math.pi) * 50 + 240)
    points.append([i, n])
    
while True:
    clock.tick(60)
    screen.fill((0, 0, 0))

    pygame.draw.lines(screen, (0, 255, 55), False, points, 1)

    # Events
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            pygame.quit()
            sys.exit()

        if event.type == KEYDOWN:
            if event.key == K_ESCAPE:
                pygame.quit()
                sys.exit()

    pygame.display.update()

---

EDIT:

Version which uses offset to animate wave

import sys
import math
import pygame
from pygame.locals import *

pygame.init()

screen = pygame.display.set_mode((500, 500))

offset = 0

clock = pygame.time.Clock()

while True:

    # - all updates (without draws) -

    points = []

    # Draw Sine Wave
    for i in range(500):
        n = int(math.sin((i+offset) / 500 * 4 * math.pi) * 50 + 240)
        points.append([i, n])

    offset += 1

    # - all draws (without updates) -

    clock.tick(60)
    screen.fill((0, 0, 0))

    pygame.draw.lines(screen, (0, 255, 55), False, points[:500], 1)

    pygame.display.update()
        
    # - events -

    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            pygame.quit()
            sys.exit()

        if event.type == KEYDOWN:
            if event.key == K_ESCAPE:
                pygame.quit()
                sys.exit()