python - Accepting only integers for TIC TAC TOE -

here's tic tac toe game have created using python..

import os os.system('cls')  = 0 #exiter def exithoja():     import sys     raw_input     sys.exit()  #displays win or draw def diswin(name,grid):     = checkwin(grid)     os.system('cls')      viewgrid(grid)      if ==1:         print name, " has won game !!"     elif == -1:         print "this match draw !!"     exithoja() #checking win or draw function def checkwin(grid):     = 0     result = 0     extra=0     in range (1,9):            #this part checks full grid.         if (grid[i] == 'x' or grid[i]=='o'):             += 1         if (grid[1] == grid[2] , grid[2] == grid[3]):             result = 1                   #this part checks win.          elif(grid[4] == grid[5] , grid[5] == grid[6]):             result = 1         elif(grid[7] == grid[8] , grid[8] == grid[9]):             result = 1          elif(grid[1] == grid[4] , grid[4] == grid[7]):             result = 1          elif(grid[2] == grid[5] , grid[5] == grid[8]):             result = 1          elif(grid[3] == grid[6] , grid[6] == grid[9]):             result = 1          elif(grid[1] == grid[5] , grid[5] == grid[9]):             result = 1          elif(grid[3] == grid[5] , grid[5] == grid[7]):             result = 1          elif(extra==9):       #this part checks draw.             result = -1      return result         #0 continue,1 win, -1 draw.   #grid print function def viewgrid(grid):     print "\n\n      .       .\n",     print "      |       |    "     in range(1,10):         if i%3==0:             print " ",         else:             print "",         print "",grid[i]," ",         if i%3 == 0:             if == 9:                 print "\n      |       |",                 print "\n      '       '"             else:                 print "\n      |       |    ",                 print "\n------+-------+-------\n",                 print "      |       |    "          else:             print "|",  #grid print function ends  #marks user choice possible ('x' or 'o' if possible, 0 if not possible) def markgrid(user,grid, place):     if grid[place] != place:         returnvalue = 0     else:         returnvalue = user     return returnvalue #end of mark grid function    #player 1 marking function part 1 def player11(name1,grid):     os.system('cls')     viewgrid(grid)     print name1, ", please enter choice grid above : ",     place = raw_input()     place = int(place,10)     if place == '.':         import sys         sys.exit()     elif place > 9 or place < 1:         place = 0     return place #player 1 marking function part 1 ends  #player 1 marking function part 2 def player12(place,grid,name1):     if place == 0:         while place==0:             place == player11(name1,grid)     grid[place] = markgrid('o',grid,place) #player 1 marking function part 2 ends   #player 2 marking function part 1 def player21(name2,grid):     os.system('cls')     viewgrid(grid)     print name2, ", please enter choice grid above : ",     place = raw_input()     place = int(place,10)     if place == '.':         import sys         sys.exit()     elif place > 9 or place < 1:         place = 0     return place #player 2 marking function part 1 ends  #player 2 marking function part 2 def player22(place,grid,name2):     if place == 0:         while place==0:             place == player21(name2,grid)     grid[place] = markgrid('x',grid,place) #player 2 marking function part 2 ends    #reset grid code starts here def gridreset(grid):     j = 0          j in range(0,10):         grid.append(j) #reset grid code ends here  #this main program, defined function def playgame():     print "\n\nuser 1 - please enter name : ",     name1 = raw_input()     print "user 2 - please enter name : ",     name2 = raw_input()     print "\n",name1,", marking o",     print "\n",name2,", marking x"     user1 = 'o'     user2 = 'x'     raw_input()     grid = []     gridreset(grid)     def player1(name1):         = player11(name1,grid)         if markgrid('o',grid,i) == 0:             player1(name1)         player12(i,grid,name1)         = checkwin(grid)         print         if i==1 or == -1:             diswin(name1,grid)         player2(name2)         return grid     def player2(name2):         = player21(name2,grid)         if markgrid('x',grid,i) == 0:             player2(name2)         player22(i,grid,name2)         = checkwin(grid)         if i==1 or == -1:             diswin(name2,grid)         player1(name1)         return grid     player1(name1)     player2(name2)     return grid #main program end  #main program execution grid = []  grid = playgame() 

the main thing left accept integers variable "place" in functions player11 , player21.. if it's not integer function called again , new value "place" assigned.. please me on how go ... in advance.. edit: user/player not given error code...

according principle seeking forgiveness better asking permission, simple try:except clause

while true:     r = raw_input('choose ')     try:         c = int(r)     except valueerror:             print 'not valid.\n'     else:         break         #this executed if no exception raised  print c 

note: else: break executed if no exception raised. if input different integer, exception raised, else:break clause not executed, not break loop , ask insert again number again. if insert number, no exception raised, 'else:break' executed , exit while loop, number still stored in variable c