code: def can_patch(self, filename):
      
      filename = abspath(filename)
      for p in self.items:
        if filename == abspath(p.source):
          return self._match_file_hunks(filename, p.hunks)
      return None
docs: Check if specified filename can be patched. Returns None if file can
      not be found among source filenames. False if patch can not be applied
      clearly. True otherwise.
  
      :returns: True, False or None