input: Write a Python class to modify the case of the string.
  class StringCaseModifier:
      def __init__(self, string):
          self.string = string
  
      def to_upper(self):
          return self.string.upper()
  
      def to_lower(self):
          return self.string.lower()
      
      def to_title(self):
          return self.string.title()
  
  assert StringCaseModifier('Hello World').to_upper()=='HELLO WORLD'
  assert StringCaseModifier('Hello World').to_lower()=='hello world'
  assert StringCaseModifier('Hello World').to_title()=='Hello World'
output: def __init__(self, string):
      self.string = string
  
  def to_upper(self):
      return self.string.upper()
  
  def to_lower(self):
      return self.string.lower()
  
  def to_title(self):
      return self.string.title()