new_contents: class Solution(object):
      def findMaxAverage(self, nums, k):
          """
          :type nums: List[int]
          :type k: int
          :rtype: float
          """
          s = sum(nums[:k])
          m = s
          for i in xrange(k, len(nums)):
              s += nums[i] - nums[i - k]
              m = max(m, s)
          return float(m) / k
  
  
subject: Add py solution for 643. Maximum Average Subarray I