In general, you shouldn’t modify library files. In this case, it is not visible because the exposed class list doesn’t include it. However, don’t modify that list! Instead:
from torch import nn

class DividedLinear(nn.Module):
  #write your code, remember to super(DividedLinear, self).__init__ 

and just use this class from here. Whether it is under torch.nn namespace won’t affect how pytorch deals with it. The important thing is that it subclasses nn.Module.