text: 
  __all__ = ['Mark', 'YAMLError', 'MarkedYAMLError']
  
  class Mark(object):
  
      def __init__(self, name, index, line, column, buffer, pointer):
          self.name = name
          self.index = index
          self.line = line
          self.column = column
          self.buffer = buffer
          self.pointer = pointer
  
      def get_snippet(self, indent=4, max_length=75):
          if self.buffer is None:
              return None
          head = ''
          start = self.pointer
          while start > 0 and self.buffer[start-1] not in u'\0\r\n\x85\u2028\u2029':
              start -= 1
              if self.pointer-start > max_length/2-1:
                  head = ' ... '
                  start += 5
                  break
          tail = ''
          end = self.pointer
          while end < len(self.buffer) and self.buffer[end] not in u'\0\r\n\x85\u2028\u2029':
              end += 1
              if end-self.pointer > max_length/2-1:
                  tail = ' ... '
                  end -= 5
                  break
          snippet = self.buffer[start:end].encode('utf-8')
          return ' '*indent + head + snippet + tail + '\n'  \
                  + ' '*(indent+self.pointer-start+len(head)) + '^'
  
      def __str__(self):
          snippet = self.get_snippet()
          where = "  in \"%s\", line %d, column %d"   \
                  % (self.name, self.line+1, self.column+1)
          if snippet is not None:
              where += ":\n"+snippet
          return where
  
  class YAMLError(Exception):
      pass
  
  class MarkedYAMLError(YAMLError):
  
      def __init__(self, context=None, context_mark=None,
              problem=None, problem_mark=None, note=None):
          self.context = context
          self.context_mark = context_mark
          self.problem = problem
          self.problem_mark = problem_mark
          self.note = note
  
      def __str__(self):
          lines = []
          if self.context is not None:
              lines.append(self.context)
          if self.context_mark is not None  \
              and (self.problem is None or self.problem_mark is None
                      or self.context_mark.name != self.problem_mark.name
                      or self.context_mark.line != self.problem_mark.line
                      or self.context_mark.column != self.problem_mark.column):
              lines.append(str(self.context_mark))
          if self.problem is not None:
              lines.append(self.problem)
          if self.problem_mark is not None:
              lines.append(str(self.problem_mark))
          if self.note is not None:
              lines.append(self.note)
          return '\n'.join(lines)
  
  