Hi, everyone. I am making a tic - tac - toe game and I am having some trouble.

As you can see I have made good progress:

```
from os import system
a = "1"; b = "2"; c = "3"; d = "4"; e = "5"; f = "6"; g = "7"; h = "8"; i = "9";
while True:
system("cls") #OS code, for linux change to "clear"
print a, b, c,"\n", d , e, f,"\n", g, h, i
u = raw_input('Enter number [X] ')
if u == "1":
a = "x"
if u == "2":
b = "x"
if u == "3":
c = "x"
if u == "4":
d = "x"
if u == "5":
e = "x"
if u == "6":
f = "x"
if u == "7":
g = "x"
if u == "8":
h = "x"
if u == "9":
i = "x"
else:
print "Please enter a valid number."
```

I haven't got round to giving player O a turn yet, but I think I have gotten off to a bad start

:(

Because now, I don't know how to continue or how the program will detect if one player has won (with 3 in a row).