def __call__(self, sample, return_str=False):
return self._tokenizer.tokenize(sample, return_str=return_str)<EOL>
Parameters
----------
sample: str
    The sentence to tokenize
return_str: bool, default False
    True: return a single string
    False: return a list of tokens

Returns
-------
ret : list of strs or str
    List of tokens or tokenized text