Update custom classes tutorial to include namespaces

Author: James Reed

advanced_source/torch_script_custom_classes.rst

@@ -78,12 +78,13 @@ Now let's take a look at how we will make this class visible to TorchScript, a p
   //   In general, you cannot register a non-specialized template
   //   class. For non-templated classes, you can just pass the
   //   class name directly as the template parameter.
-  // - The single parameter to ``torch::class_()`` is a
-  //   string indicating the name of the class. This is the name
-  //   the class will appear as in both Python and TorchScript.
-  //   For example, our MyStackClass class would appear as ``torch.classes.MyStackClass``.
+  // - The arguments passed to the constructor make up the "qualified name"
+  //   of the class. In this case, the registered class will appear in
+  //   Python and C++ as `torch.classes.my_classes.MyStackClass`. We call
+  //   the first argument the "namespace" and the second argument the
+  //   actual class name.
   static auto testStack =
-    torch::class_<MyStackClass<std::string>>("MyStackClass")
+    torch::class_<MyStackClass<std::string>>("my_classes", "MyStackClass")
         // The following line registers the contructor of our MyStackClass
         // class that takes a single `std::vector<std::string>` argument,
         // i.e. it exposes the C++ method `MyStackClass(std::vector<T> init)`.
@@ -217,7 +218,7 @@ demonstrates that:
   #
   # This instantiation will invoke the MyStackClass(std::vector<T> init) constructor
   # we registered earlier
-  s = torch.classes.MyStackClass(["foo", "bar"])
+  s = torch.classes.my_classes.MyStackClass(["foo", "bar"])
 
   # We can call methods in Python
   s.push("pushed")
@@ -233,16 +234,16 @@ demonstrates that:
   # For now, we need to assign the class's type to a local in order to
   # annotate the type on the TorchScript function. This may change
   # in the future.
-  MyStackClass = torch.classes.MyStackClass
+  MyStackClass = torch.classes.my_classes.MyStackClass
 
   @torch.jit.script
   def do_stacks(s : MyStackClass): # We can pass a custom class instance to TorchScript
-      s2 = torch.classes.MyStackClass(["hi", "mom"]) # We can instantiate the class
+      s2 = torch.classes.my_classes.MyStackClass(["hi", "mom"]) # We can instantiate the class
       s2.merge(s) # We can call a method on the class
       return s2.clone(), s2.top()  # We can also return instances of the class
                                    # from TorchScript function/methods
 
-  stack, top = do_stacks(torch.classes.MyStackClass(["wow"]))
+  stack, top = do_stacks(torch.classes.my_classes.MyStackClass(["wow"]))
   assert top == "wow"
   for expected in ["wow", "mom", "hi"]:
       assert stack.pop() == expected
@@ -265,7 +266,7 @@ instantiates and calls a method on our MyStackClass class:
           super().__init__()
 
       def forward(self, s : str) -> str:
-          stack = torch.classes.MyStackClass(["hi", "mom"])
+          stack = torch.classes.my_classes.MyStackClass(["hi", "mom"])
           return stack.pop() + s
 
   scripted_foo = torch.jit.script(Foo())
@@ -435,7 +436,7 @@ an attribute, you'll get the following error:
   class Foo(torch.nn.Module):
     def __init__(self):
         super().__init__()
-        self.stack = torch.classes.MyStackClass(["just", "testing"])
+        self.stack = torch.classes.my_classes.MyStackClass(["just", "testing"])
 
     def forward(self, s : str) -> str:
         return self.stack.pop() + s
@@ -447,7 +448,7 @@ an attribute, you'll get the following error:
 .. code-block:: shell
 
   $ python export_attr.py
-  RuntimeError: Cannot serialize custom bound C++ class __torch__.torch.classes.MyStackClass. Please define serialization methods via def_pickle for this class. (pushIValueImpl at ../torch/csrc/jit/pickler.cpp:128)
+  RuntimeError: Cannot serialize custom bound C++ class __torch__.torch.classes.my_classes.MyStackClass. Please define serialization methods via def_pickle for this class. (pushIValueImpl at ../torch/csrc/jit/pickler.cpp:128)
 
 This is because TorchScript cannot automatically figure out what information
 save from your C++ class. You must specify that manually. The way to do that
@@ -466,7 +467,7 @@ Here is an example of how we can update the registration code for our
 .. code-block:: cpp
 
   static auto testStack =
-    torch::class_<MyStackClass<std::string>>("MyStackClass")
+    torch::class_<MyStackClass<std::string>>("my_classes", "MyStackClass")
         .def(torch::init<std::vector<std::string>>())
         .def("top", [](const c10::intrusive_ptr<MyStackClass<std::string>>& self) {
           return self->stack_.back();
@@ -528,7 +529,7 @@ now run successfully:
   class Foo(torch.nn.Module):
       def __init__(self):
           super().__init__()
-          self.stack = torch.classes.MyStackClass(["just", "testing"])
+          self.stack = torch.classes.my_classes.MyStackClass(["just", "testing"])
 
       def forward(self, s : str) -> str:
           return self.stack.pop() + s
@@ -562,7 +563,7 @@ example of how to do that:
   static auto instance_registry = torch::RegisterOperators().op(
   torch::RegisterOperators::options()
       .schema(
-          "foo::manipulate_instance(__torch__.torch.classes.MyStackClass x) -> __torch__.torch.classes.MyStackClass Y")
+          "foo::manipulate_instance(__torch__.torch.classes.my_classes.MyStackClass x) -> __torch__.torch.classes.my_classes.MyStackClass Y")
       .catchAllKernel<decltype(manipulate_instance), &manipulate_instance>());
 
 Refer to the `custom op tutorial <https://pytorch.org/tutorials/advanced/torch_script_custom_ops.html>`_
@@ -575,7 +576,7 @@ Once this is done, you can use the op like the following example:
   class TryCustomOp(torch.nn.Module):
       def __init__(self):
           super(TryCustomOp, self).__init__()
-          self.f = torch.classes.MyStackClass(["foo", "bar"])
+          self.f = torch.classes.my_classes.MyStackClass(["foo", "bar"])
 
       def forward(self):
           return torch.ops.foo.manipulate_instance(self.f)