Python Basic control flow errors

Question

When I run this code, it enters a while loop and checks every turn whether or not on_title_screen==True. If it is true, the program will continue to check for input, but if it is false, the loop will refresh the screen and begin the game. However, when start is clicked, and on_title_screen=False, the game still captures mouse input, and does not display the bird that it should.

import random
import pygame
from pygame import *
import math
import sys
#Presets for window
size=width,height=500,500
Ag=-9.80665
clock = pygame.time.Clock()
white=(255,255,255)
blue=(0,0,255)
red=(255,0,0)
gray_bgColor=(190,193,212)
#Initialise pygame Surface as screen
pygame.init()
pygame.font.init()
screen=pygame.display.set_mode(size)
pygame.display.set_caption("Flappy Kid")
#Game Presets
vY=0
xPos,yPos=200,100
score=0

on_title_screen=True

def falling_loop():
    for event in pygame.event.get():
        if event.type==pygame.KEYDOWN:
            if event.key==pygame.K_UP:
                vY=-10
    if yPos>height-50:
        yPos=100
    vY+=1
    yPos+=vY

class graphics():
    #Holds the methods for loading/displaying graphics
    def load_images(self):
        #Loads the background and sprite images
        self.background_image=pygame.image.load("flappy_background.png").convert()
        self.bird_image=pygame.image.load("flappy_sprite.jpg").convert()
        screen.set_colorkey(white)
        self.birdHitBox=self.bird_image.get_rect()
    def show_background(self):
        #blits the background
        screen.blit(self.background_image,[0,0])
    def refresh_display(self):
        #updates the display
        screen.blit(self.background_image,[xPos,yPos],self.birdHitBox)
        falling_loop()
        screen.blit(self.bird_image,[xPos,yPos])

class titleScreen():
    #Holds the methods for the title screen/menu
    def title(self):
        #Sets up the title
        titleText="Flappy Game"
        titlePos=(0,0)
        currentFont=pygame.font.SysFont("arialms",30,bold=True,italic=True)
        renderTitle=currentFont.render(titleText,1,blue,gray_bgColor)
        self.titlex,self.titley=currentFont.size(titleText)
        screen.blit(renderTitle,titlePos)
    def start(self):
        #Sets up the start Button
        startText="Start Game"
        self.startPos=(0,self.titley)
        currentFont=pygame.font.SysFont("arialms",25,bold=False,italic=False)
        renderStart=currentFont.render(startText,1,blue,gray_bgColor)
        self.startx,self.starty=currentFont.size(startText)
        self.start_rect = pygame.Rect(self.startPos[0],self.titley,self.startx,self.starty)
        screen.blit(renderStart,self.startPos)
    def quit(self):
        #Sets up the quit button
        quitText="Quit"
        self.quitPos=(0,self.starty+self.titley)
        currentFont=pygame.font.SysFont("arialms",25,bold=False,italic=False)
        renderQuit=currentFont.render(quitText,1,red,gray_bgColor)
        self.quitx,self.quity=currentFont.size(quitText)
        self.quit_rect = pygame.Rect(self.quitPos[0],self.titley+self.starty,self.quitx,self.quity)
        screen.blit(renderQuit,self.quitPos)
    def get_click(self):
        #Gets mouse click and processes outcomes
        for event in pygame.event.get():
            if event.type==pygame.MOUSEBUTTONDOWN:
                x,y=pygame.mouse.get_pos()
                #Tests for start:
                if self.start_rect.collidepoint(x,y):
                    print("start")
                    on_title_screen=False
                elif self.quit_rect.collidepoint(x,y):
                    print("quit")
                    sys.exit()

titleC=titleScreen()
graphicsC=graphics()
def setupTitle():
    #bundles all title_screen functions
    titleC.title()
    titleC.start()
    titleC.quit()

def main():
    graphicsC.load_images()
    graphicsC.show_background()
    setupTitle()
    while True:
        clock.tick(30)
        if on_title_screen==False:
            graphicsC.refresh_display()
        elif on_title_screen==True:
            titleC.get_click()
        pygame.display.flip()

main()

Answer 1

I think @TessellatingHeckler is right, on_title_screen is a shadow variable, not the same.

In this code, there is nowhere that on_title_screen (global) could ever be set to False.

A more powerful answer though is to explain how to find the problem. I strongly recommend using pdb or ipdb. In this case, I would put one just inside of the while loop and make sure that the variables are what I think they should be.