物体检测框架之mmdetection源码阅读（3）

本篇要解决的问题是如何通过configs文件来构建detector的问题，话说上一回讲到了构建detector前要在mmcv中注册模型。那么如何注册模型呢？暂且切回到上篇的代码的前几行

from mmcv.cnn import MODELS as MMCV_MODELS
from mmcv.utils import Registry

MODELS = Registry('models', parent=MMCV_MODELS)

那么我们深入mmcv查看第三行代码的意思，跳转到Registry

import inspect
import warnings
from functools import partial

from .misc import is_seq_of


def build_from_cfg(cfg, registry, default_args=None):
    """Build a module from config dict.

    Args:
        cfg (dict): Config dict. It should at least contain the key "type".
        registry (:obj:`Registry`): The registry to search the type from.
        default_args (dict, optional): Default initialization arguments.

    Returns:
        object: The constructed object.
    """
    if not isinstance(cfg, dict):
        raise TypeError(f'cfg must be a dict, but got {type(cfg)}')
    if 'type' not in cfg:
        if default_args is None or 'type' not in default_args:
            raise KeyError(
                '`cfg` or `default_args` must contain the key "type", '
                f'but got {cfg}\n{default_args}')
    if not isinstance(registry, Registry):
        raise TypeError('registry must be an mmcv.Registry object, '
                        f'but got {type(registry)}')
    if not (isinstance(default_args, dict) or default_args is None):
        raise TypeError('default_args must be a dict or None, '
                        f'but got {type(default_args)}')

    args = cfg.copy()

    if default_args is not None:
        for name, value in default_args.items():
            args.setdefault(name, value)

    obj_type = args.pop('type')
    if isinstance(obj_type, str):
        obj_cls = registry.get(obj_type)
        if obj_cls is None:
            raise KeyError(
                f'{obj_type} is not in the {registry.name} registry')
    elif inspect.isclass(obj_type):
        obj_cls = obj_type
    else:
        raise TypeError(
            f'type must be a str or valid type, but got {type(obj_type)}')
    try:
        return obj_cls(**args)
    except Exception as e:
        # Normal TypeError does not print class name.
        raise type(e)(f'{obj_cls.__name__}: {e}')


class Registry:
    """A registry to map strings to classes.

    Registered object could be built from registry.
    Example:
        >>> MODELS = Registry('models')
        >>> @MODELS.register_module()
        >