[fix] fix bugs

metric-codebleu.py

@@ -104,6 +104,19 @@ class codebleu(evaluate.Metric):
     ):
         """Returns the scores"""
 
+        if isinstance(references, str):
+            references = [references]
+
+        if isinstance(references[0], str):
+            references = [[ref] for ref in references]
+
+        if isinstance(predictions, str):
+            predictions = [predictions]
+
+        assert isinstance(references, list)
+        assert isinstance(predictions, list)
+        assert len(references) == len(predictions), "The number of predictions and references must be the same."
+
         return calc_codebleu(
             references=references,
             predictions=predictions,