list changes while doing with functions

def matMinor3x3(mat,a,b):
    minor=[[0,0],[0,0]]
    temp1=mat[:]
    for i in range(0,3):
        del temp1[i][b-1]
    del temp1[a-1]
    return temp1

A=[[1,2,3],[4,5,6],[7,8,9]]
print A,matMinor3x3(A,1,1),A

This is my code. I searched about questions that asks list of variables changing. Their answer was to make copy with copy=original[:]. But I tired, and it doesn't work. Split columns and reassemble them to make copy doesn't work either. Please help me. I was making inverse matrix code...