разделяйте ваши назначения на разные строки:
if(player == 'Player1' and marker == 'X'):
temp_player1 = 'Player1'
player1_marker = 'X'
temp_player2 = 'Player2'
player2_marker = '0'
elif(player == 'Player1' and marker == '0'):
temp_player1 = 'Player1'
player1_marker = '0'
temp_player2 = 'Player2'
player2_marker = 'X'
elif(player == 'Player2' and marker == 'X'):
temp_player1 = 'Player1'
player1_marker = '0'
temp_player2 = 'Player2'
player2_marker = 'X'
elif(player == 'Player2' and marker == '0'):
temp_player1 = 'player1'
player1_marker = 'X'
temp_player2 = 'Player2'
player2_marker = '0'
else:
pass
вы должны прочитать о том, как работает отступ в python, когда несколько операторов в одной строке не очень распространены для удобства чтения