you can use enumerate to do the same with much simpler code

```
class Solution:
# @param {integer[]} nums
# @param {integer} k
# @return {boolean}
def containsNearbyDuplicate(self, nums, k):
sequence = list(enumerate(nums))
sequence.sort(key = lambda x: x[1])
for i in xrange(len(sequence) - 1):
if (sequence[i][1] == sequence[i+1][1]) and (abs(sequence[i][0] - sequence[i+1][0]) <= k):
return True
return False
```