python - Prompting the user for correct input - tic tac toe game -

i'm working on program simulates tic-tac-toe game between 2 players. program want far, except part ask players input. want program check whether (3 x 3) grid contains mark (for example, 'x' or 'o'), , keep prompting same player correct input before switching turns. here have far:

board = [         0, 1, 2,         3, 4, 5,         6, 7, 8         ]  def main():     print_instructions()     start = str(input("your game begin. press 'q' if want quit, or 'k' proceed: "))     while start != "q":         get_input1()         get_input2()   def display_board(board):     print(board[0], "|" , board[1] , "|" , board[2])     print("----------")     print(board[3] , "|" , board[4] , "|" , board[5])     print("----------")     print(board[6] , "|" , board[7] , "|" , board[8])   def print_instructions():     print("please use following cell numbers make move: ")     display_board(board)   def get_input1():     userinput = input("the first player marks 'x'. type integer between 0 8 indiciate want move: ")     userinput = int(userinput)     if userinput < 0 or userinput > 8 or board[userinput] == "x" or board[userinput] == "o":         print("wrong input! cannot move there! ")     else:         board[userinput] = "x"      display_board(board)  def get_input2():     userinput = input("turn of second player. mark 'o'. move? type integer between 0 , 8: ")     userinput = int(userinput)     if userinput < 0 or userinput > 8 or board[userinput] == "x" or board[userinput] == "o":         print("wrong input! cannot move there! ")     else:         board[userinput] = "o"      display_board(board)    main() 

i still have write part program decides winner is, want def get_input function right first. how can check valid input in case? tried using while loop, 1 kept prompting user indefinitely without terminating (maybe did wrong there). appreciated.

maybe forgot take input in while loop! try this.

while userinput < 0 or userinput > 8 or board[userinput] == "x" or board[userinput] == "o":     print("wrong input! cannot move there! ")     userinput = input("please give valid move.") board[userinput] = "x"