old_contents: class SourceCoordinate(object):
  
      _immutable_fields_ = ['_start_line', '_start_column', '_char_idx']
  
      def __init__(self, start_line, start_column, char_idx):
          self._start_line   = start_line
          self._start_column = start_column
          self._char_idx     = char_idx
  
      def get_start_line(self):
          return self._start_line
  
      def get_start_column(self):
          return self._start_column
  
  
  class SourceSection(object):
  
      _immutable_fields_ = ['_source', '_identifier', '_coord', '_char_length']
  
      def __init__(self, source = None, identifier = None, coord = None,
                   char_length = None, file = None, source_section = None):
          if source_section:
              self._source      = source_section._source
              self._coord       = source_section._coord
              self._char_length = source_section._char_length
              self._file        = source_section._file
          else:
              self._source      = source
              self._coord       = coord
              self._char_length = char_length
              self._file        = file
          self._identifier  = identifier
  
      def __str__(self):
          return "%s:%d:%d" % (self._file, self._coord.get_start_line(),
                               self._coord.get_start_column())
  
new_contents: class SourceCoordinate(object):
  
      _immutable_fields_ = ['_start_line', '_start_column', '_char_idx']
  
      def __init__(self, start_line, start_column, char_idx):
          self._start_line   = start_line
          self._start_column = start_column
          self._char_idx     = char_idx
  
      def get_start_line(self):
          return self._start_line
  
      def get_start_column(self):
          return self._start_column
  
  
  class SourceSection(object):
  
      _immutable_fields_ = ['_source', '_identifier', '_coord', '_char_length']
  
      def __init__(self, source = None, identifier = None, coord = None,
                   char_length = 0, file_name = None, source_section = None):
          if source_section:
              self._source      = source_section._source
              self._coord       = source_section._coord
              self._char_length = source_section._char_length
              self._file        = source_section._file
          else:
              self._source      = source
              self._coord       = coord
              self._char_length = char_length
              self._file        = file_name
          self._identifier  = identifier
  
      def __str__(self):
          return "%s:%d:%d" % (self._file, self._coord.get_start_line(),
                               self._coord.get_start_column())
  
subject: Initialize char_length with a number