Ensure cachedproperty descriptor picks up docstrings

Closes-Bug: #1325677

Change-Id: I6366dea5458adec30e945a9834e15da946813461

taskflow/tests/unit/test_utils.py

@@ -16,6 +16,7 @@
 
 import collections
 import functools
+import inspect
 import sys
 import time
 
@@ -370,6 +371,25 @@ class CachedPropertyTest(test.TestCase):
         self.assertRaises(AttributeError, try_set, a)
         self.assertEqual('b', a.b)
 
+    def test_documented_property(self):
+
+        class A(object):
+            @misc.cachedproperty
+            def b(self):
+                """I like bees."""
+                return 'b'
+
+        self.assertEqual("I like bees.", inspect.getdoc(A.b))
+
+    def test_undocumented_property(self):
+
+        class A(object):
+            @misc.cachedproperty
+            def b(self):
+                return 'b'
+
+        self.assertEqual(None, inspect.getdoc(A.b))
+
 
 class AttrDictTest(test.TestCase):
     def test_ok_create(self):

taskflow/utils/misc.py

@@ -187,15 +187,18 @@ class cachedproperty(object):
         if inspect.isfunction(fget):
             self._fget = fget
             self._attr_name = "_%s" % (fget.__name__)
+            self.__doc__ = getattr(fget, '__doc__', None)
         else:
             self._attr_name = fget
             self._fget = None
+            self.__doc__ = None
 
     def __call__(self, fget):
         # If __init__ received a string then this will be the function to be
         # wrapped as a property (if __init__ got a function then this will not
         # be called).
         self._fget = fget
+        self.__doc__ = getattr(fget, '__doc__', None)
         return self
 
     def __set__(self, instance, value):
@@ -205,6 +208,8 @@ class cachedproperty(object):
         raise AttributeError("can't delete attribute")
 
     def __get__(self, instance, owner):
+        if instance is None:
+            return self
         try:
             return getattr(instance, self._attr_name)
         except AttributeError: