old_contents: class Error(Exception):
      def __init__(self):
          self.message = 'bla'
  
      def __str__(self):
          return repr(self.message)
  
  
  class ConfigFileError(Exception):
      def __init__(self, file):
          self.file = file
          self.message = 'Config file not exists "%s".' % self.file
  
  
  class ConfigKeyError(Exception):
      def __init__(self, key):
          self.key = key
          self.message = 'Config with key "%s" not set.' % self.key
  
new_contents: class Error(Exception):
      def __init__(self):
          self.message = ''
  
      def __str__(self):
          return repr(self.message)
  
  
  class ConfigFileError(Exception):
      def __init__(self, file):
          self.file = file
          self.message = 'Config file not exists "%s".' % self.file
  
  
  class ConfigKeyError(Exception):
      def __init__(self, key):
          self.key = key
          self.message = 'Config with key "%s" not set.' % self.key
  
subject: Remove placeholder