Logic Error in a matrix roll dice program in Python

Question

I have the following code for a simple game that lets player1 and player2 take turns to roll two six sided dice(die). On reaching 49 (the last number in the matrix) a player will win. Players start at 1 and then move up the number that is rolled (total of both die).

I have three errors ( logic errors ) in my code that I need some help with.

1) The winner functionality doesn't work. If a player reaches 49 or is close (see output at the end) it doesn't logically allow them to win. (just keep pressing enter to run a test and see the peculiar output pasted below). Player 1 AND Player 2 can reach 49 but it doesn't take them to the "winner()" module. Why? I have used ">=" correctly or have I not?

Having said that, in one test: Player 2 reached 49, and it didn't go to the winner() module:

    Press Enter to continue
Player 2, it's your turn to roll the dice: Press r to roll:>>>
Player2: You rolled a: 4 and a 6 which gives you a: 10
You have moved 10 spaces to position:....... 49

2)On exiting the program completely and starting again, the values of player1position and player2position are reset to 0 and it works. But if I just go to main() to replay the game, these values are not reset . I don't fully understand the usage and declaration of global variables and initialisation. Can anyone shed some light and an explanation/suggestion would help

3) Negative numbers aren't dealt with accurately. If on any turn a player throw TWO of the SAME number, they are meant to go back for the number rolled. eg if 2 and 2 rolled, the player goes back 4. However, if the player goes back when they are 5, 10 spaces, to -5, the next turn doesn't add up the total for player1position or player2position and the counting is messed up . I've tried various fixes and I'd be interested in any comments, suggestions and improvements.

The erroneous output is below:

First, this is the matrix:

*************LOADING GAME******************
Welcome: player1 and player2
[43, 44, 45, 46, 47, 48, 49]
[42, 41, 40, 39, 38, 37, 36]
[29, 30, 31, 32, 33, 34, 35]
[28, 27, 26, 25, 24, 23, 22]
[15, 16, 17, 18, 19, 20, 21]
[14, 13, 12, 11, 10, 9, 8]
[1, 2, 3, 4, 5, 6, 7]

The code that is relevant is as follows:

import sys
import csv
import random 
def main():
    startscreen()

def loadstartgame(player1,player2):
    with open("messages.txt","r") as f:
        idnumber="1"
        fReader=csv.reader(f)
        for row in fReader:
            for field in row:
                if field==idnumber:
                                       print(row[2])


        start=input("Start?:>>")

        if start=="s" or "S":

            callmatrix(player1,player2,7)

def startscreen():
    print("******************************Welcome to CONQUER THE MATRIX****************************")
    print("You can take on a friend in this game")
    player1=input("Enter name of Player 1: ")
    player2=input("Enter name of Player 2: ")
    print("Welcome ...", player1,"and, ", player2, "...Are you ready?")
    response=input("Yes or No? Player 1 - perhaps you could confirm please: ")
    if response=="yes" or "Yes" or "yEs" or "YeS":
        loadstartgame(player1, player2)
    else:
        sys.exit()



def matrix(n): 
    grid = [[1 + i + n * j for i in range(n)] for j in range(n)] 
    for row in grid[1::2]:
        row.reverse()    
    return grid[::-1][:]

def callmatrix(player1,player2, n):
    print("*************LOADING GAME******************")
    print("Welcome:", player1,"and", player2)
    for i in matrix(n):
            print(i)
    playing = True
    playerturns(player1,player2,playing)


def playerturns(player1,player2,playing):

    print(" - - - - - - - - - - ")
    print("Press Enter to continue")

    while(playing):     
        roll=input()
        if roll=="":
            RollTwoDiceP1(player1,player2)

        else:
            break
    RollTwoDiceP2(player1,player2)


global player1position #declare a local variable called player1position
player1position=0 #set the global variable before the start of this sub to 0
def RollTwoDiceP1(player1,player2):
    global player1position

    print("player1position in PLAYER1ROLL", player1position)
    #print("player1position at stat of RollTwoDicep1", player1position) #a test that prints the current value of player 1 position
    turn=input("Player 1, it's your turn to roll the dice: Press r to roll:>>>")
    die1=random.randint(1,6)
    die2=random.randint(1,6)
    #die1=5 #for testing purposes
    #die2=5 #for testing purposes
    roll=die1+die2    
    print("Player1: You rolled a:", die1, "and a", die2, "which gives you a:", roll)
    playing = False

    matrixlist=matrix(7)

    if die1==die2:
        gobackspacesP1(roll,player1,player2)
    else:
        print("You have moved", roll, "spaces to position:.......",matrixlist[6][0]+(roll+player1position))
    #print("playerposition plus roll:", player1position+roll) #a test that prints the playerposition+roll - this always comes up to 1 more than it should do on the location, so below substract 1, to make it produce an accurate location on the matrix for a particular roll
    player1position=matrixlist[6][0]+(roll+player1position)
    if player1position>=49:
                winner()
    else:
                playerturns(player1,player2,playing)

#global player1position
#global player2position
def gobackspacesP1(roll,player1,player2):
    global player1position
    if player1position<=1:
        player1position=0
        print("Oh dear - sorry you are now back to square 1 - literally!")
    else:
        print("Oh dear -you are now back on the matrix to position:", (1+player1position)-roll)
        matrixlist=matrix(7)
        #new player1position=the first playerposition minus the roll (rather than add it) and + 1 (as the initial position is always 1)
        player1position=1+(player1position-roll)
        #player1position=matrixlist[6][0]+(roll+player1position)-roll
    playing=False
    print("player1position in goback", player1position)
    playerturns(player1,player2,playing)



def gobackspacesP2(roll,player1,player2):
    global player2position
    if player2position<=1:
        player2position=0
        print("Oh dear - sorry you are now back to square 1 - literally!")
    else:
        print("Oh dear -you are now back on the matrix to position:", (1+player2position)-roll)
        matrixlist=matrix(7)
        #new player1position=the first playerposition minus the roll (rather than add it) and + 1 (as the initial position is always 1)
        player2position=1+(player2position-roll)
        #player1position=matrixlist[6][0]+(roll+player1position)-roll
    playing=True
    print("player2position in goback", player2position)
    playerturns(player1,player2,playing)


global player2position
player2position=0
def RollTwoDiceP2(player1,player2):
    global player2position
#Remember you need to add the functioanlity for a double identical dice roll to this subroutine for Player2 as well. 
    turn=input("Player 2, it's your turn to roll the dice: Press r to roll:>>>")
    die1=random.randint(1,6)
    die2=random.randint(1,6)
    roll=die1+die2    
    print("Player2: You rolled a:", die1, "and a", die2, "which gives you a:", roll)
    playing = True
    matrixlist=matrix(7)

    if die1==die2:
        gobackspacesP2(roll,player1,player2)
    else:
        print("You have moved", roll, "spaces to position:.......",matrixlist[6][0]+(roll+player2position))
    #print("playerposition plus roll:", player1position+roll) #a test that prints the playerposition+roll - this always comes up to 1 more than it should do on the location, so below substract 1, to make it produce an accurate location on the matrix for a particular roll
    player2position=matrixlist[6][0]+(roll+player2position)
    if player2position>=49:
                winner()
    else:
                playerturns(player1,player2,playing)

def winner():
    print("Ahh, it appears you have won! Congratulations!")
    sys.exit()

def easygrid():
    grid=[[43,44,45,46,47,48,49],[42,41,40,39,38,37,36],[29,30,31,32,33,34,35],[28, 27, 26, 25,24,23,22], [15,16,17, 18, 19, 20, 21], [14, 13, 12, 11, 10, 9, 8], [1, 2, 3,4,5,6,7]]
    for i in grid:
        print(i)
main()

I'd also be interested in any comments about my use of global variables and how best to use/not use them in this context.

I do not want a class based solution, so the answer would have to be a fix to this.

ERRONEOUS OUTPUT 1 (only player 2 wins, even though Player 1 should have won) LAST FEW ROLLS leading up to the win:

player1position in PLAYER1ROLL 38
Player 1, it's your turn to roll the dice: Press r to roll:>>>
Player1: You rolled a: 3 and a 5 which gives you a: 8
You have moved 8 spaces to position:....... 47
- - - - - - - - - - 
Press Enter to continue
Player 2, it's your turn to roll the dice: Press r to roll:>>>
Player2: You rolled a: 6 and a 5 which gives you a: 11
You have moved 11 spaces to position:....... 43
- - - - - - - - - - 
Press Enter to continue

player1position in PLAYER1ROLL 46
Player 1, it's your turn to roll the dice: Press r to roll:>>>
Player1: You rolled a: 3 and a 5 which gives you a: 8
You have moved 8 spaces to position:....... 55
- - - - - - - - - - 
Press Enter to continue
Player 2, it's your turn to roll the dice: Press r to roll:>>> 
Player2: You rolled a: 6 and a 1 which gives you a: 7
You have moved 7 spaces to position:....... 50
You've won! Congratulations!

Answer 1

The bug was in this line: (in the RollTwoDice1 and RollTwoDice2 subs)

player1position=matrixlist[6][0]+(roll+player1position)

the matrixlist[6][0] was added an erroneous +1, which when removed sorted the logic error.

Also: (in the gobacktospaces subs)

 player2position=1+(player2position-roll)

It had an extra -1 in it, which kept skewing the results for both the winner functionality and the adding up.