Fix tuple_losses bug caused by Python bug.

PiperOrigin-RevId: 168386341

tensorflow/contrib/gan/python/losses/python/tuple_losses_impl.py

@@ -73,7 +73,21 @@ def _args_to_gan_model(loss_fn):
   default_args_dict = dict(zip(args_with_defaults, defaults))
 
   def new_loss_fn(gan_model, **kwargs):  # pylint:disable=missing-docstring
-    gan_model_dict = gan_model._asdict()
+    def _asdict(namedtuple):
+      """Returns a namedtuple as a dictionary.
+
+      This is required because `_asdict()` in Python 3.x.x is broken in classes
+      that inherit from `collections.namedtuple`. See
+      https://bugs.python.org/issue24931 for more details.
+
+      Args:
+        namedtuple: An object that inherits from `collections.namedtuple`.
+
+      Returns:
+        A dictionary version of the tuple.
+      """
+      return {k: getattr(namedtuple, k) for k in namedtuple._fields}
+    gan_model_dict = _asdict(gan_model)
 
     # Make sure non-tuple required args are supplied.
     args_from_tuple = set(argspec.args).intersection(set(gan_model._fields))

tensorflow/contrib/gan/python/losses/python/tuple_losses_test.py

@@ -79,6 +79,21 @@ class ArgsToGanModelTest(test.TestCase):
     # If `arg3` were not set properly, this value would be different.
     self.assertEqual(-1 + 2 * 2 + 3 * 4, loss)
 
+  def test_works_with_child_classes(self):
+    """`args_to_gan_model` should work with classes derived from namedtuple."""
+    tuple_type = collections.namedtuple('fake_type', ['arg1', 'arg2'])
+
+    class InheritedType(tuple_type):
+      pass
+    def args_loss(arg1, arg2, arg3=3):
+      return arg1 + 2 * arg2 + 3 * arg3
+
+    loss_fn = tfgan_losses._args_to_gan_model(args_loss)
+    loss = loss_fn(InheritedType(arg1=-1, arg2=2), arg3=4)
+
+    # If `arg3` were not set properly, this value would be different.
+    self.assertEqual(-1 + 2 * 2 + 3 * 4, loss)
+
 
 class ConsistentLossesTest(test.TestCase):