TIC TAC TOE

#To check whether the computer or Human has won"
def check(l):
#The z here is just a counter to see whether you have completed all the three squares
    z=0
#List a are all the ways you can win
    a=[[1,2,3],[4,5,6],[7,8,9],[1,4,7],[2,5,6],[3,6,9],[1,5,9],[3,5,7]]
    for i in a:
#The for loop extracts through the List a
        z=0
        for j in i:
#This for loop extracts through i,which is an element of list a
           if j in l:
               z=z+1
#If z is 3 it means that the person has completed all the squares
        if z==3:
            break

    if z==3:
        return(3)
#This function shows the board currently
def board(l1,l2):
    a=['-','-','-','-','-','-','-','-','-']
#This for loop is to check where the computer and the human has placed their mark
    for i in range (1,10):
#This if checks where the mark is and places it on the respective squares
        if i in l1:
#This puts cross where the human has marked and knot for where the computer has marked in the respective list position
            a[i-1]="X"
        if i in l2:
            a[i-1]="O"
    print(a[0],a[1],a[2])
    print(a[3],a[4],a[5])
    print(a[6],a[7],a[8])


import random
print("The layout is ")
print()
print(" 1 2 3")
print(" 4 5 6")
print(" 7 8 9")
#Here l is all the valid moves
l=[1,2,3,4,5,6,7,8,9]
l1=[]
l2=[]
for i in range (1,6):
    print("Your valid positions are ",l)
    while True:
        a=float(input("Enter where you would like to place the cross "))
        if a not in l:
            print("Wrong input,enter again")
            continue
        if a in l:
            break
#Here the append function appends your move in list1/l1
    l1.append(int(a))
    print(l1)
#Here the l.remove removes one of the valid position,which is a. a is the position chosen by you
    l.remove(a)
#Calling the check function defined above
    y=check(l1)
#As the check function returns 3 if all the 3 sqaures are marked
    if y==3:
        print("You win ")
#Board is the function defined above
        board(l1,l2)
        break
    if i==5:
        break
#random.choice chooses a random option from list L
    c=random.choice(l)
#Here the l.remove removes one of the valid position,which is a. a is the position chosen by the computer
    l.remove(c)
    l2.append(c)
    print("I placed my knot in number ",c)
    board(l1,l2)
    y=check(l2)
#As the check function returns 3 if all the 3 sqaures are marked
    if y==3:
        print("I win ")
        board(l1,l2)
        break