new_contents: class Solution(object):
  
      def checkValidString(self, s):
          """
          :type s: str
          :rtype: bool
          """
          lowest, highest = 0, 0
          for c in s:
              if c == '(':
                  lowest += 1
                  highest += 1
              elif c == ')':
                  if lowest > 0:
                      lowest -= 1
                  highest -= 1
                  if highest < 0:
                      return False
              else:
                  if lowest > 0:
                      lowest -= 1
                  highest += 1
          return lowest == 0
  
subject: Add py solution for 678. Valid Parenthesis String