lib/python3.9/site-packages/caffe2/python/layers/__init__.py

from importlib import import_module
import pkgutil
import sys
from . import layers


def import_recursive(package):
    """
    Takes a package and imports all modules underneath it
    """

    pkg_dir = package.__path__
    module_location = package.__name__
    for (_module_loader, name, ispkg) in pkgutil.iter_modules(pkg_dir):
        module_name = "{}.{}".format(module_location, name)  # Module/package
        module = import_module(module_name)
        if ispkg:
            import_recursive(module)


def find_subclasses_recursively(base_cls, sub_cls):
    cur_sub_cls = base_cls.__subclasses__()
    sub_cls.update(cur_sub_cls)
    for cls in cur_sub_cls:
        find_subclasses_recursively(cls, sub_cls)


import_recursive(sys.modules[__name__])

model_layer_subcls = set()
find_subclasses_recursively(layers.ModelLayer, model_layer_subcls)

for cls in list(model_layer_subcls):
    layers.register_layer(cls.__name__, cls)