code: def datafile(filename, mode="rb", format=None):
      
  
      filename = os.path.expanduser(filename)
      base, ext = os.path.splitext(filename)
  
      if format is None:
          hc = get_handler_class(ext)
      else:
          hc = _handler_map.get(format)
          if hc is None:
              raise ValueError('Format {} not supported.'.format(format))
  
      fd = open(filename, mode)
  
      handler = hc(fd)
      return handler
docs: Initialize the appropriate
      :py:class:`~chemlab.io.iohandler.IOHandler` for a given file
      extension or file format.
  
      The *datafile* function can be conveniently used to quickly read
      or write data in a certain format::
  
          >>> handler = datafile("molecule.pdb")
          >>> mol = handler.read("molecule")
          # You can also use this shortcut
          >>> mol = datafile("molecule.pdb").read("molecule")
  
      **Parameters**
  
      filename: str
            Path of the file to open.
      format: str or None
            When different from *None*, can be used to specify a
            format identifier for that file. It should be used when
            the extension is ambiguous or when there isn't a specified
            filename. See below for a list of the formats supported by chemlab.