add Wikitext2 + wikitext103 data

lm_eval/tasks/wikitext.py

+import numpy as np
+from scipy.stats import pearsonr, spearmanr
+from sklearn.metrics import f1_score, matthews_corrcoef
+from tqdm import auto as tqdm_lib
+from . common import NLP_TASK, simple_accuracy_metric, yesno
+
+class WikiText103(NLP_TASK):
+    NLP_PATH = "wikitext"
+    NLP_NAME = "wikitext-103-raw-v1"
+
+    def fewshot_description(self):
+        return ""
+
+    def doc_to_text(self, doc, include_target=True):
+        return doc['text']
+    def evaluate(self, docs, lm, provide_description, num_fewshot):
+        pass
+
+
+class WikiText2(NLP_TASK):
+    NLP_PATH = "wikitext"
+    NLP_NAME = "wikitext-2-raw-v1"
+
+    def fewshot_description(self):
+        return ""
+
+    def doc_to_text(self, doc, include_target=True):
+        return doc['text']
+    def evaluate(self, docs, lm, provide_description, num_fewshot):
+        pass
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