add test

pandas/_libs/properties.pyx

@@ -17,8 +17,11 @@ cdef class CachedProperty(object):
         self.__doc__ = getattr(func, '__doc__', None)
 
     def __get__(self, obj, typ):
-        # Get the cache or set a default one if needed
+        if obj is None:
+            # accessed on the class, not the instance
+            return self
 
+        # Get the cache or set a default one if needed
         cache = getattr(obj, '_cache', None)
         if cache is None:
             try:

pandas/tests/test_lib.py

@@ -3,6 +3,7 @@
 import pytest
 
 import numpy as np
+from pandas import Index
 from pandas._libs import lib, writers as libwriters
 import pandas.util.testing as tm
 
@@ -198,3 +199,8 @@ def test_get_reverse_indexer(self):
         result = lib.get_reverse_indexer(indexer, 5)
         expected = np.array([4, 2, 3, 6, 7], dtype=np.int64)
         tm.assert_numpy_array_equal(result, expected)
+
+
+def test_cache_readonly_preserve_docstrings():
+    # GH18197
+    assert Index.hasnans.__doc__ is not None