How to check for duplicates with less time in a list over 9000 elements by python

um trying to check whether there are duplicate values exists in an integer list by python . this was successful and I found that the execution time getting higher when the size of the list getting increase. How may I improve the run time of the following logic?

def containsDuplicate( nums):
    if len(nums) < 2:
        return False
    cnt = 0
    flag = False
    length = len(nums)
    while cnt < length:
        p = cnt + 1
        while p < length:
            if nums[cnt] == nums[p]:
                flag = True
                break
            p += 1
        cnt += 1
    return flag

Answer

You could use a set:

>>> lst = [1, 2, 3]
>>> len(set(lst)) != len(lst)
False
>>> lst = [1, 2, 2]
>>> len(set(lst)) != len(lst)
True

EDIT: a faster version, as pointed out in the comments:

>>> lst = [3] + list(range(10**4))
>>> seen = set()
>>> any(x in seen or seen.add(x) for x in lst)
True
>>> seen
set([0, 1, 2, 3])