How to create MS Paint clone with Python and pygame

Question

As I see it, there are two ways to handle mouse events to draw a picture.

The first is to detect when the mouse moves and draw a line to where the mouse is, shown he

Answer 1

Not blitting at each loop step can improve the speed of the drawing (using this code adapted from the previous one allow to remove lag problem on my machine)

import pygame, random

screen = pygame.display.set_mode((800,600))

draw_on = False
last_pos = (0, 0)
color = (255, 128, 0)
radius = 10

def roundline(srf, color, start, end, radius=1):
    dx = end[0]-start[0]
    dy = end[1]-start[1]
    distance = max(abs(dx), abs(dy))
    for i in range(distance):
        x = int( start[0]+float(i)/distance*dx)
        y = int( start[1]+float(i)/distance*dy)
        pygame.display.update(pygame.draw.circle(srf, color, (x, y), radius))

try:
    while True:
        e = pygame.event.wait()
        if e.type == pygame.QUIT:
            raise StopIteration
        if e.type == pygame.MOUSEBUTTONDOWN:
            color = (random.randrange(256), random.randrange(256), random.randrange(256))
            pygame.draw.circle(screen, color, e.pos, radius)
            draw_on = True
        if e.type == pygame.MOUSEBUTTONUP:
            draw_on = False
        if e.type == pygame.MOUSEMOTION:
            if draw_on:
                pygame.display.update(pygame.draw.circle(screen, color, e.pos, radius))
                roundline(screen, color, e.pos, last_pos,  radius)
            last_pos = e.pos
        #pygame.display.flip()

except StopIteration:
    pass

pygame.quit()