From 0cf85dec98f46c3f15d0eab61f82084e1b985086 Mon Sep 17 00:00:00 2001
From: llllllllll <joe@quantopian.com>
Date: Tue, 24 Nov 2015 15:07:27 -0500
Subject: [PATCH] BUG: fix issues with sentinel

---
 tests/utils/test_sentinel.py | 48 ++++++++++++++++++++++++++++++++++++
 zipline/utils/sentinel.py    | 34 ++++++++++++++-----------
 2 files changed, 68 insertions(+), 14 deletions(-)
 create mode 100644 tests/utils/test_sentinel.py

diff --git a/tests/utils/test_sentinel.py b/tests/utils/test_sentinel.py
new file mode 100644
index 00000000..ebf06be0
--- /dev/null
+++ b/tests/utils/test_sentinel.py
@@ -0,0 +1,48 @@
+from copy import copy, deepcopy
+from pickle import loads, dumps
+from unittest import TestCase
+from weakref import ref
+
+from zipline.utils.sentinel import sentinel
+
+
+class SentinelTestCase(TestCase):
+    def tearDown(self):
+        sentinel._cache.clear()  # don't pollute cache.
+
+    def test_name(self):
+        self.assertEqual(sentinel('a').__name__, 'a')
+
+    def test_doc(self):
+        self.assertEqual(sentinel('a', 'b').__doc__, 'b')
+
+    def test_doc_differentiates(self):
+        self.assertIsNot(sentinel('a', 'b'), sentinel('a', 'c'))
+
+    def test_memo(self):
+        self.assertIs(sentinel('a'), sentinel('a'))
+
+    def test_copy(self):
+        a = sentinel('a')
+        self.assertIs(copy(a), a)
+
+    def test_deepcopy(self):
+        a = sentinel('a')
+        self.assertIs(deepcopy(a), a)
+
+    def test_repr(self):
+        self.assertEqual(
+            repr(sentinel('a')),
+            "sentinel('a')",
+        )
+
+    def test_new(self):
+        with self.assertRaises(TypeError):
+            type(sentinel('a'))()
+
+    def test_pickle_roundtrip(self):
+        a = sentinel('a')
+        self.assertIs(loads(dumps(a)), a)
+
+    def test_weakreferencable(self):
+        ref(sentinel('a'))
diff --git a/zipline/utils/sentinel.py b/zipline/utils/sentinel.py
index 02e9c6e2..bcccca2d 100644
--- a/zipline/utils/sentinel.py
+++ b/zipline/utils/sentinel.py
@@ -7,19 +7,25 @@ import sys
 
 
 def sentinel(name, doc=None):
-    @object.__new__   # bind a single instance to the name 'NotSpecified'
-    class result(object):
+    try:
+        return sentinel._cache[name, doc]  # memoized
+    except KeyError:
+        pass
+
+    @object.__new__   # bind a single instance to the name 'Sentinel'
+    class Sentinel(object):
         __doc__ = doc
         __slots__ = ('__weakref__',)
+        __name__ = name
 
         def __new__(cls):
-            raise TypeError("Can't construct new instances of %s" % name)
+            raise TypeError("Can't construct new instances of %r" % name)
 
         def __repr__(self):
-            return name
+            return 'sentinel(%r)' % name
 
         def __reduce__(self):
-            return name
+            return sentinel, (name, doc)
 
         def __deepcopy__(self, _memo):
             return self
@@ -27,14 +33,14 @@ def sentinel(name, doc=None):
         def __copy__(self):
             return self
 
-    cls = type(result)
-    cls.__name__ = name
+    cls = type(Sentinel)
     try:
         # traverse up one frame to find the module where this is defined
-        cls.__module__ = sys._getframe(1).f_globals.get(
-            '__name__',
-            '__main__',
-        )
-    except (AttributeError, ValueError):
-        pass
-    return result
+        cls.__module__ = sys._getframe(1).f_globals['__name__']
+    except (AttributeError, ValueError, KeyError):
+        # Couldn't get the name from the calling scope, just use None.
+        cls.__module__ = None
+
+    sentinel._cache[name, doc] = Sentinel  # cache result
+    return Sentinel
+sentinel._cache = {}