Python: random choice on matrix without selecting the number on the same line

I have a problem because I would like realise a matrix by a random selection with replacement from the previous column without selecting the number that is on the same line as this element.

For example:

#I create a matrix "pop" where there are numbers in the first and second column and where there are zeros on the other columns
tab = np.array([[3, 2, 1, 0, 4, 6], [9, 8, 7, 8, 2, 0]]) 
tab1=tab.transpose()
pop=np.zeros((6,8),int)
pop[:,0:2]=tab1

#I create a function "cuntage" which complete the matrix "pop" by a 
#random sampling with replacement  from the second previous column 
def countage (a):
    for i in range (0,6):
        pop[i,a]=np.random.choice(pop[:,(a-2)],1,replace=True)


# loope to complete the array "pop"
for r in range(2,8):
    countage(r)

pop

But the problem is that I would like select, by a random choice from second previous column, each element of the matrix but without selecting the number that is on the same line as this element.

For example, in the matrix pop, the element pop[0,2] is select in pop[1:6,0].

Thanks for your responses!!

;-)