new_contents: # Time:  O(n)
  # Space: O(1)
  
  # Implement function ToLowerCase() that has a string parameter str,
  # and returns the same string in lowercase.
  
  class Solution(object):
      def toLowerCase(self, str):
          """
          :type str: str
          :rtype: str
          """
          return "".join([chr(ord('a')+ord(c)-ord('A')) 
                          if 'A' <= c <= 'Z' else c for c in str])
  
subject: Create to-lower-case.py