Example:
  class MyModule(nn.Module):
      def __init__(self):
          super(MyModule, self).__init__()
          self.params = nn.ParameterDict({
                  'left': nn.Parameter(torch.randn(5, 10)),
                  'right': nn.Parameter(torch.randn(5, 10))
          })

      def forward(self, x, choice):
          x = self.params[choice].mm(x)
          return x

clear()
  Remove all items from the ParameterDict.

copy()
  Returns a copy of this "ParameterDict" instance.

  Return type:
     *ParameterDict*

fromkeys(keys, default=None)
  Return a new ParameterDict with the keys provided

  Parameters:
     * **keys** (*iterable**, **string*) -- keys to make the new
       ParameterDict from

     * **default** (*Parameter**, **optional*) -- value to set for
       all keys

  Return type:
     *ParameterDict*

get(key, default=None)