Add append method for nn.Sequential (#71326)

Summary:
Partially addresses #71249, and potentially supersedes #20274.

Pull Request resolved: #71326

Reviewed By: cpuhrsch

Differential Revision: D33855047

Pulled By: jbschlosser

fbshipit-source-id: a3a682e206f93b4c52bc3405e2f7b26aea6635ea
(cherry picked from commit c0b27bb)

test/test_nn.py

@@ -1521,6 +1521,17 @@ def test_Sequential_delitem(self):
         del n[1::2]
         self.assertEqual(n, nn.Sequential(l1, l3))
 
+    def test_Sequential_append(self):
+        l1 = nn.Linear(10, 20)
+        l2 = nn.Linear(20, 30)
+        l3 = nn.Linear(30, 40)
+        l4 = nn.Linear(40, 50)
+        n = nn.Sequential(l1, l2, l3)
+        n2 = n.append(l4)
+        self.assertEqual(n, nn.Sequential(l1, l2, l3, l4))
+        self.assertEqual(n2, nn.Sequential(l1, l2, l3, l4))
+        self.assertEqual(nn.Sequential(l1).append(l2).append(l4), nn.Sequential(l1, l2, l4))
+
     def test_ModuleList(self):
         modules = [nn.ReLU(), nn.Linear(5, 5)]
         module_list = nn.ModuleList(modules)

torch/nn/modules/container.py

@@ -141,6 +141,15 @@ def forward(self, input):
             input = module(input)
         return input
 
+    def append(self, module: Module) -> 'Sequential':
+        r"""Appends a given module to the end.
+
+        Args:
+            module (nn.Module): module to append
+        """
+        self.add_module(str(len(self)), module)
+        return self
+
 
 class ModuleList(Module):
     r"""Holds submodules in a list.