Solved by ptrblck in post #4 
              
              
                nn.MaxPool2d is a module, so you would have to pass the tensor to it: 
pool = nn.MaxPool2d(kernel_size, stride)
x = pool(previous_conv)

It looks like you are trying to pass the tensor directly to the constructor of the class. 
The functional approach (using F.max_pool2d) should also work.