Warn instead of raising in BERT and GPT-2 tokenizers as well, to allow for pre-caching of tokens

pytorch_pretrained_bert/tokenization.py

@@ -101,7 +101,7 @@ class BertTokenizer(object):
         for token in tokens:
             ids.append(self.vocab[token])
         if len(ids) > self.max_len:
-            raise ValueError(
+            logger.warning(
                 "Token indices sequence length is longer than the specified maximum "
                 " sequence length for this BERT model ({} > {}). Running this"
                 " sequence through BERT will result in indexing errors".format(len(ids), self.max_len)