import pygame, time
from pygame import *
pygame.init()

hod = 'n'
a = 0

def menu():
    if a == 0:
        menu_fon = image.load('img/menu_fon.png').convert_alpha()
    menu_fon.blit(okno)
    a = 1
    return a

okno = display.set_mode((800, 600))
while hod != 'c':
    for event in pygame.event.get():
        if event.type == QUIT: 
            hod = 'c'
    if hod == 'n':
        menu()
    display.flip()
    time.wait(41)

if a == 0:
UnboundLocalError: local variable 'a' referenced before assignment

def menu():
    global a
    if a == 0:

# -*- coding: utf-8 -*-
import sys
a = 0
b = 1
def c():
    if a == 0:
        d = b + 1
        print(d)

while 1:
    c()
    sys.exit()