code: def realpath(self, filename):
          
          if self.filesystem.is_windows_fs:
              return self.abspath(filename)
          filename = make_string_path(filename)
          path, ok = self._joinrealpath(filename[:0], filename, {})
          return self.abspath(path)
docs: Return the canonical path of the specified filename, eliminating any
          symbolic links encountered in the path.