class Registry:
    def __init__(self, name, scope=None, parent=None):
        self.name = name
        self.scope = scope
        self.parent = parent
        self._module_dict = {}
    def register_module(self, name=None):
        def _register(cls):
            module_name = name or cls.__name__
            if module_name in self._module_dict:
                raise KeyError(f'{module_name} is already registered in {self.scope}::{self.name}')
            self._module_dict[module_name] = cls
            return cls
        return _register
    def get(self, name):
        if name in self._module_dict:
            return self._module_dict[name]
        elif self.parent:
            return self.parent.get(name)
        else:
            raise KeyError(f'{name} is not registered in {self.scope}::{self.name} and no parent registry to fallback.')
    def build(self, cfg):
        module_name = cfg['type']
        module_cls = self.get(module_name)
        return module_cls(**{k: v for k, v in cfg.items() if k != 'type'})

from torch import nn
# 創(chuàng)建父注冊(cè)表
MODELS = Registry('models', scope='mmengine')
# 注冊(cè)一個(gè)模塊到父注冊(cè)表
@MODELS.register_module()
class ResNet(nn.Module):
    def __init__(self, layers):
        self.layers = layers
    def forward(self, x):
        return x
# 創(chuàng)建子注冊(cè)表，指定 MODELS 為父注冊(cè)表
DETECTORS = Registry('detectors', scope='mmengine', parent=MODELS)
# 注冊(cè)一個(gè)模塊只到子注冊(cè)表
@DETECTORS.register_module()
class FasterRCNN(nn.Module):
    def __init__(self, num_classes):
        self.num_classes = num_classes
    def forward(self, x):
        return x
# 從子注冊(cè)表構(gòu)建 ResNet 實(shí)例，盡管它是在父注冊(cè)表中注冊(cè)的
resnet_instance = DETECTORS.build({'type': 'ResNet', 'layers': 50})
print(resnet_instance)
# 直接從子注冊(cè)表構(gòu)建 FasterRCNN 實(shí)例
fasterrcnn_instance = DETECTORS.build({'type': 'FasterRCNN', 'num_classes': 80})
print(fasterrcnn_instance)