human
I found an interesting problem on https://leetcode.com/problems/number-of-sub-arrays-with-odd-sum/:
Given an array of integers arr. Return the number of sub-arrays with odd sum.
As the answer may grow large, the answer must be computed modulo 10^9 + 7.
 
Example 1:
Input: arr = [1,3,5]
Output: 4
Explanation: All sub-arrays are [[1],[1,3],[1,3,5],[3],[3,5],[5]]
All sub-arrays sum are [1,4,9,3,8,5].
Odd sums are [1,9,3,5] so the answer is 4.

Example 2:
Input: arr = [2,4,6]
Output: 0
Explanation: All sub-arrays are [[2],[2,4],[2,4,6],[4],[4,6],[6]]
All sub-arrays sum are [2,6,12,4,10,6].
All sub-arrays have even sum and the answer is 0.

Example 3:
Input: arr = [1,2,3,4,5,6,7]
Output: 16

Example 4:
Input: arr = [100,100,99,99]
Output: 4

Example 5:
Input: arr = [7]
Output: 1

 
Constraints:

1 <= arr.length <= 10^5
1 <= arr[i] <= 100

I tried it in Python, but could not do it. Can you solve it?
assistant
#Here is the Python program you requested.

class Solution:
    def numOfSubarrays(self, arr: List[int]) -> int:
        s, d, ans = 0, 0, 0
        for n in arr:
                if n%2:
                    s, d = d, s
                    s += 1
                else:
                    d += 1
                ans += s
                #print(n, ans)
        return ans%1000000007