first complete duplicate pair of a list, not the fastest

first_dupe.py

def firstDupe(a):
    """
    Finding the first occurrence of any duplicates with the first second occurrence of a value
    as long as params are met.
    Returns -1 if outside params.
    """
    if len(a) == len(set(a)):
        return -1

    indices = [a.index(i) for i in a]
    ilist = list()
    if 1 <= len(a) <= 10 ** 5:  # param 1
        for i in range(0, len(a)):
            if indices[i] <= len(a):  # param 2
                if indices[i] != i:
                    ilist.append((i, a[i]))  # ilist appends the second index occurrence

            # of the dupe value
            else:
                return -1
    else:
        return -1
    #print(ilist)
    if len(ilist) == 0:
        return -1
    n = [(z, x) for z, x in ilist]
    print(n, min(n)[1])
    return min(n)[1]


firstDupe([6, 8, 4, 9, 1, 4, 12, 5, 3, 5, 10, 12])