import pygame
from pygame.locals import *

pygame.init()

def draw_lines():
  screen = pygame.display.set_mode((640, 480))
  pygame.display.set_caption("Draw lines with the mouse")
  background = pygame.Surface(screen.get_size())
  background.fill((255, 255, 255))

  clock = pygame.time.Clock()
  done = False
  lineWidth = 3
  while(not done):
    for event in pygame.event.get():
      if event.type == pygame.QUIT:
        done = True
      elif event.type == KEYDOWN and event.key == K_ESCAPE:
        done = True
      elif event.type == pygame.MOUSEBUTTONDOWN:
        lineStart = pygame.mouse.get_pos()
      elif event.type == pygame.MOUSEBUTTONUP:
        lineEnd = pygame.mouse.get_pos()
        pygame.draw.line(background, (0,0,0), lineStart, lineEnd, lineWidth)
    screen.blit(background, (0, 0))
    pygame.display.flip()
    
draw_lines()
pygame.quit()