Allow pickling of builtin methods

cloudpickle/cloudpickle.py

@@ -196,6 +196,26 @@ def save_function(self, obj, name=None):
             if getattr(themodule, name, None) is obj:
                 return self.save_global(obj, name)
 
+        # a builtin_function_or_method which comes in as an attribute of some
+        # object (e.g., object.__new__, itertools.chain.from_iterable) will end
+        # up with modname "__main__" and so end up here. But these functions
+        # have no __code__ attribute in CPython, so the handling for 
+        # user-defined functions below will fail.
+        # So we pickle them here using save_reduce; have to do it differently
+        # for different python versions.
+        if not hasattr(obj, '__code__'):
+            if PY3:
+                if sys.version_info < (3, 4):
+                    raise pickle.PicklingError("Can't pickle %r" % obj)
+                else:
+                    rv = obj.__reduce_ex__(self.proto)
+            else:
+                if hasattr(obj, '__self__'):
+                    rv = (getattr, (obj.__self__, name))
+                else:
+                    raise pickle.PicklingError("Can't pickle %r" % obj)
+            return Pickler.save_reduce(self, obj=obj, *rv)
+
         # if func is lambda, def'ed at prompt, is in main, or is nested, then
         # we'll pickle the actual function object rather than simply saving a
         # reference (as is done in default pickler), via save_function_tuple.

tests/cloudpickle_test.py

@@ -5,6 +5,7 @@
 import pickle
 import sys
 import functools
+import itertools
 import platform
 import textwrap
 
@@ -291,5 +292,16 @@ def test_Ellipsis(self):
     def test_NotImplemented(self):
         self.assertEqual(NotImplemented, pickle_depickle(NotImplemented))
 
+    @pytest.mark.skipif((3, 0) < sys.version_info < (3, 4),
+                        reason="fails due to pickle behavior in Python 3.0-3.3")
+    def test_builtin_function_without_module(self):
+        on = object.__new__
+        on_depickled = pickle_depickle(on)
+        self.assertEqual(type(on_depickled(object)), type(object()))
+
+        fi = itertools.chain.from_iterable
+        fi_depickled = pickle_depickle(fi)
+        self.assertEqual(list(fi([[1, 2], [3, 4]])), [1, 2, 3, 4])
+
 if __name__ == '__main__':
     unittest.main()