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

For the first problem, you need have a background, even if its just a color. I had the same problem with a replica pong game i made. Here is an example of a replica paint program I made, left click to draw, right click to erase, click on the color image to choose a color, and up button to clear screen:

import os
os.environ['SDL_VIDEO_CENTERED'] = '1'
from pygamehelper import *
from pygame import *
from pygame.locals import *
from vec2d import *
from math import e, pi, cos, sin, sqrt
from random import uniform

class Starter(PygameHelper):
    def __init__(self):
        self.w, self.h = 800, 600
        PygameHelper.__init__(self, size=(self.w, self.h), fill=((255,255,255)))

        self.img= pygame.image.load("colors.png")
        self.screen.blit(self.img, (0,0))

        self.drawcolor= (0,0,0)
        self.x= 0

    def update(self):
        pass

    def keyUp(self, key):
        if key==K_UP:
            self.screen.fill((255,255,255))
            self.screen.blit(self.img, (0,0))




    def mouseUp(self, button, pos):
        pass

    def mouseMotion(self, buttons, pos, rel):
        if pos[1]>=172: 
            if buttons[0]==1:
                #pygame.draw.circle(self.screen, (0,0,0), pos, 5)
                pygame.draw.line(self.screen, self.drawcolor, pos, (pos[0]-rel[0], pos[1]-rel[1]),5)                
            if buttons[2]==1:
                pygame.draw.circle(self.screen, (255,255,255), pos, 30)
            if buttons[1]==1:
                #RAINBOW MODE
                color= self.screen.get_at((self.x, 0))
                pygame.draw.line(self.screen, color, pos, (pos[0]-rel[0], pos[1]-rel[1]), 5)

                self.x+= 1
                if self.x>172: self.x=0

        else:
            if pos[0]<172:
                if buttons[0]==1:
                    self.drawcolor= self.screen.get_at(pos)
                    pygame.draw.circle(self.screen, self.drawcolor, (250, 100), 30)

    def draw(self):
        pass
        #self.screen.fill((255,255,255))
        #pygame.draw.circle(self.screen, (0,0,0), (50,100), 20)

s = Starter()
s.mainLoop(40)