Find duplicate integers in Python

find_duplicates.py

def find_duplicates(nums):
    sorted_nums = sorted(nums)
    last = None
    dups = []

    for n in sorted_nums:
        if last and n == last:
            try:
                last_dup = dups[-1]
            except IndexError:
                last_dup = n + 1

            if last_dup != n:
                dups.append(n)

        last = n

    return dups