I am looking on how I can improve my writing style and/or how to simplify how I write my code.

    # USER: TCG
    # Tic Tac Toe (User vs Computer)

    import random

    def place(num,x):
        # Returns all the moves made
        for i in range(len(x)):
            if x[i] == num:
                pos = x.index(num)
                return x[(pos + 1)]
        return str(num)

    def print_grid(move,player,x):

        pos_list.extend([move,player])
    
        # Grid on which the player and computer play on            
        grid = ["","-------------\n",
            "|",place(1,pos_list),"|",place(2,pos_list),"|",place(3,pos_list),"|\n",
            "|---+---+---|\n",
            "|",place(4,pos_list),"|",place(5,pos_list),"|",place(6,pos_list),"|\n",
            "|---+---+---|\n",
            "|",place(7,pos_list),"|",place(8,pos_list),"|",place(9,pos_list),"|\n",
            "-------------\n"]
        if x == 2:
            # Only prints one the player has made a move
            print '\n', ' '.join(grid)
        
    def winner(x,player,xx):

        # Checks if there is a winner (Really messy, could do with code simplifying)
        if ((1 in x and 4 in x and 7 in x)or(1 in x and 2 in x and 3 in x)or(2 in x and 5 in x and 8 in x)or(3 in x and 6 in x and 9 in x)or
        (4 in x and 5 in x and 6 in x)or(7 in x and 8 in x and 9 in x)or(1 in x and 5 in x and 9 in x)or(3 in x and 5 in x and 7 in x)):
        # If prevents the A.I part from printing the statemnt
            if xx <> 1:
                print '\n'*5,"\'%s\'" %player, "HAS WON!"
            return 1 == 1
    
    def computer_AI_part(listx):
        global computer_move

        # Chceks all possible values which the player can and enter to win and blocks it
        for x in range(1,10):
            if x not in pos_list:
                listx.append(x)
                if (winner(listx,'Computer',1)) == True:
                    del listx[-1]
                    computer_move = x
                    return 1
                del listx[-1]

    def computer_and_player():
        global computer_move,pos_list,player_list,computer_list
        replay,draw = 0,0

        while True:

            # Replay's the game
            if replay == 1:
                restart = raw_input("Would you like to replay?: ")
                if restart == "yes":
                    pass
                else:
                    return
            else:
                print "\nTic Tac Toe - Computer vs You", '\n'*2,"Computer goes first\n"
            
            replay,computer_move,players_move,loop_count,pos_list,player_list,computer_list = 0,0,0,0,[],[],[]
        
            for each in "XXXXX":
                loop_count += 1
            
                # Computer's Move
                if computer_AI_part(computer_list) or computer_AI_part(player_list) == 1:
                    pass     
                else:
                    while True:
                        computer_move = random.randint(1,9)
                        if computer_move in pos_list:
                            continue
                        break
                computer_list.append(computer_move)
                # Prints Grid
                print_grid(computer_move,'O',2)

                if loop_count == 5:
                    if winner(player_list,'player',2) == True or winner(computer_list,'Computer',2) == True:
                        pass
                    else:
                        print "Match Was a draw!"
                    replay = 1
                    break

                # Checks winner
                if winner(computer_list,'Computer',2) == True:
                    replay = 1
                    break

                # Player's Move
                while True:
                    try:
                        players_move = int(raw_input("\n\'%s\' Enter a value from the grid to plot your move: " %each))
                        if players_move in pos_list or players_move < 1 or players_move > 9:
                            print "Enter an available number that's between 1-9"
                            continue
                        break
                    except:
                        print "Enter a number"
                
                player_list.append(players_move)
                # Sets player's move for printing
                print_grid(players_move,each,1)

                # Checks winner again
                if winner(player_list,'player',1) == True:
                    print_grid(players_move,each,2)
                    winner(player_list,'player',2)
                    replay = 1
                    break
        
    if __name__ == "__main__":
        computer_and_player()

Update: [new version](https://gist.github.com/overlordofdoom1/78b36febd124afc169f0720b75710e72)