title: Writing PyTorch class in Cython
body: <p>I'm trying to find examples of a PyTorch <code>nn.Module</code> class written in Cython for speed but haven't found anything. Suppose I have the below class written in Python, what would the best Cython translation be?</p>
  <pre><code>class Actor(nn.Module):
      def __init__(self, state_size, action_size, hidden_size):
          super(Actor, self).__init__()
          self.l1 = nn.Linear(state_size, hidden_size)
          self.l2 = nn.Linear(hidden_size, hidden_size)
          self.l3 = nn.Linear(hidden_size, hidden_size)
          self.l4 = nn.Linear(hidden_size, action_size)
          self.log_std = nn.Parameter(-0.5 * torch.ones(action_size, dtype=torch.float32))
  
      def forward(self, x):
          x = torch.relu(self.l1(x))
          x = torch.relu(self.l2(x))
          x = torch.relu(self.l3(x))
          mu = self.l4(x)
          return mu
  
      def dist(self, mu):
          pi = Normal(mu, torch.exp(self.log_std))
          return pi
  
      def log_prob(self, pi, action):
          return pi.log_prob(action).sum(axis=-1)
  </code></pre>