Initializes a Module lazily (similar to a lazy __init__).

setup is called once lazily on a module instance when a module is bound, immediately before any other methods like __call__ are invoked, or before a setup-defined attribute on self is accessed.

This can happen in three cases:

  1. Immediately when invoking apply(), init() or init_and_output().

  2. Once the module is given a name by being assigned to an attribute of another module inside the other module’s setup method (see __setattr__()):

    class MyModule(nn.Module):
      def setup(self):
        submodule = Conv(...)
        # Accessing `submodule` attributes does not yet work here.
        # The following line invokes `self.__setattr__`, which gives
        # `submodule` the name "conv1".
        self.conv1 = submodule
        # Accessing `submodule` attributes or methods is now safe and
        # either causes setup() to be called once.
  3. Once a module is constructed inside a method wrapped with compact(), immediately before another method is called or setup defined attribute is accessed.