allow driver to run in PYTHON_MODE, which is equivalent to serial Python

test/runtest.py

@@ -377,5 +377,26 @@ class ReferenceCountingTest(unittest.TestCase):
 
     services.cleanup()
 
+class PythonModeTest(unittest.TestCase):
+
+  def testObjRefAliasing(self):
+    services.start_singlenode_cluster(driver_mode=ray.PYTHON_MODE)
+
+    xref = test_functions.test_alias_h()
+    self.assertTrue(np.alltrue(xref == np.ones([3, 4, 5]))) # remote functions should return by value
+    self.assertTrue(np.alltrue(xref == ray.get(xref))) # ray.get should be the identity
+    y = np.random.normal(size=[11, 12])
+    self.assertTrue(np.alltrue(y == ray.put(y))) # ray.put should be the identity
+
+    # make sure objects are immutable, this example is why we need to copy
+    # arguments before passing them into remote functions in python mode
+    aref = test_functions.python_mode_f()
+    self.assertTrue(np.alltrue(aref == np.array([0, 0])))
+    bref = test_functions.python_mode_g(aref)
+    self.assertTrue(np.alltrue(aref == np.array([0, 0]))) # python_mode_g should not mutate aref
+    self.assertTrue(np.alltrue(bref == np.array([1, 0])))
+
+    services.cleanup()
+
 if __name__ == "__main__":
     unittest.main()

test/test_functions.py

@@ -85,3 +85,13 @@ def throw_exception_fct2():
 @ray.remote([float], [int, str, np.ndarray])
 def throw_exception_fct3(x):
   raise Exception("Test function 3 intentionally failed.")
+
+# test Python mode
+@ray.remote([], [np.ndarray])
+def python_mode_f():
+  return np.array([0, 0])
+
+@ray.remote([np.ndarray], [np.ndarray])
+def python_mode_g(x):
+  x[0] = 1
+  return x