diff --git a/fastNLP/io/loader/coreference.py b/fastNLP/io/loader/coreference.py
index b4493571..6e2344d2 100644
--- a/fastNLP/io/loader/coreference.py
+++ b/fastNLP/io/loader/coreference.py
@@ -1,3 +1,5 @@
+"""undocumented"""
+
 from ...core.dataset import DataSet
 from ..file_reader import _read_json
 from ...core.instance import Instance
diff --git a/fastNLP/io/pipe/coreference.py b/fastNLP/io/pipe/coreference.py
index 836b251d..bb40ca55 100644
--- a/fastNLP/io/pipe/coreference.py
+++ b/fastNLP/io/pipe/coreference.py
@@ -1,3 +1,5 @@
+"""undocumented"""
+
 __all__ = [
     "CoreferencePipe"