Updating __getitem__ and __len__ for containers (pytorch#1544)

Author: dasguptar

torch/nn/modules/container.py

@@ -50,13 +50,18 @@ def __init__(self, *args):
                 self.add_module(str(idx), module)
 
     def __getitem__(self, idx):
-        if idx < 0 or idx >= len(self._modules):
+        if not (-len(self) <= idx < len(self)):
             raise IndexError('index {} is out of range'.format(idx))
+        if idx < 0:
+            idx += len(self)
         it = iter(self._modules.values())
         for i in range(idx):
             next(it)
         return next(it)
 
+    def __len__(self):
+        return len(self._modules)
+
     def forward(self, input):
         for module in self._modules.values():
             input = module(input)
@@ -92,6 +97,8 @@ def __init__(self, modules=None):
             self += modules
 
     def __getitem__(self, idx):
+        if not (-len(self) <= idx < len(self)):
+            raise IndexError('index {} is out of range'.format(idx))
         if idx < 0:
             idx += len(self)
         return self._modules[str(idx)]
@@ -161,6 +168,8 @@ def __init__(self, parameters=None):
             self += parameters
 
     def __getitem__(self, idx):
+        if not (-len(self) <= idx < len(self)):
+            raise IndexError('index {} is out of range'.format(idx))
         if idx < 0:
             idx += len(self)
         return self._parameters[str(idx)]