<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def set_from_file(self, filename: str, is_padded: bool = True, oov_token: str = DEFAULT_OOV_TOKEN, namespace: str = "tokens"):
 """ If you already have a vocabulary file for a trained model somewhere, and you really want to use that vocabulary file instead of just setting the vocabulary from a dataset, for whatever reason, you can do that with this method. You must specify the namespace to use, and we assume that you want to use padding and OOV tokens for this. Parameters filename : ``str`` The file containing the vocabulary to load. It should be formatted as one token per line, with nothing else in the line. The index we assign to the token is the line number in the file (1-indexed if ``is_padded``, 0-indexed otherwise). Note that this file should contain the OOV token string! is_padded : ``bool``, optional (default=True) Is this vocabulary padded? For token / word / character vocabularies, this should be ``True``; while for tag or label vocabularies, this should typically be ``False``. If ``True``, we add a padding token with index 0, and we enforce that the ``oov_token`` is present in the file. oov_token : ``str``, optional (default=DEFAULT_OOV_TOKEN) What token does this vocabulary use to represent out-of-vocabulary characters? This must show up as a line in the vocabulary file. When we find it, we replace ``oov_token`` with ``self._oov_token``, because we only use one OOV token across namespaces. namespace : ``str``, optional (default="tokens") What namespace should we overwrite with this vocab file? """

        if is_padded:
            self._token_to_index[namespace] = {self._padding_token: 0}
            self._index_to_token[namespace] = {0: self._padding_token}
        else:
            self._token_to_index[namespace] = {}
            self._index_to_token[namespace] = {}
        with codecs.open(filename, 'r', 'utf-8') as input_file:
            lines = input_file.read().split('\n')
            # Be flexible about having final newline or not
            if lines and lines[-1] == '':
                lines = lines[:-1]
            for i, line in enumerate(lines):
                index = i + 1 if is_padded else i
                token = line.replace('@@NEWLINE@@', '\n')
                if token == oov_token:
                    token = self._oov_token
                self._token_to_index[namespace][token] = index
                self._index_to_token[namespace][index] = token
        if is_padded:
            assert self._oov_token in self._token_to_index[namespace], "OOV token not found!"