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()
>>> class ResNet:
>>> pass
>>> resnet = MODELS.build(dict(type='ResNet'))
Please refer to https://mmcv.readthedocs.io/en/latest/registry.html for
advanced useage.
Args:
name (str): Registry name.
build_func(func, optional): Build function to construct instance from
Registry, func:`build_from_cfg` is used if neither ``parent`` or
``build_func`` is specified. If ``parent`` is specified and
``build_func`` is not given, ``build_func`` will be inherited
from ``parent``. Default: None.
parent (Registry, optional): Parent registry. The class registered in
children registry could be built from parent. Default: None.
scope (str, optional): The scope of registry. It is the key to search
for children registry. If not specified, scope will be the name of
the package where class is defined, e.g. mmdet, mmcls, mmseg.
Default: None.
"""
def __init__(self, name, build_func=None, parent=None, scope=None):
self._name = name
self._module_dict = dict()
self._children = dict()
self._scope = self.infer_scope() if scope is None else scope
# self.build_func will be set with the following priority:
# 1. build_func
# 2. parent.build_func
# 3. build_from_cfg
if build_func is None:
if parent is not None:
self.build_func = parent.build_func
else:
self.build_func = build_from_cfg
else:
self.build_func = build_func
if parent is not None:
assert isinstance(parent, Registry)
parent._add_children(self)
self.parent = parent
else:
self.parent = None
def __len__(self):
return len(self._module_dict)
def __contains__(self, key):
return self.get(key) is not None
def __repr__(self):
format_str = self.__class__.__name__ + \
f'(name={self._name}, ' \
f'items={self._module_dict})'
return format_str
@staticmethod
def infer_scope():
"""Infer the scope of registry.
The name of the package where registry is defined will be returned.
Example:
# in mmdet/models/backbone/resnet.py
>>> MODELS = Registry('models')
>>> @MODELS.register_module()
>>> class ResNet:
>>> pass
The scope of ``ResNet`` will be ``mmdet``.
Returns:
scope (str): The inferred scope name.
"""
# inspect.stack() trace where this function is called, the index-2
# indicates the frame where `infer_scope()` is called
filename = inspect.getmodule(inspect.stack()[2][0]).__name__
split_filename = filename.split('.')
return split_filename[0]
@staticmethod
def split_scope_key(key):
"""Split scope and key.
The first scope will be split from key.
Examples:
>>> Registry.split_scope_key('mmdet.ResNet')
'mmdet', 'ResNet'
>>> Registry.split_scope_key('ResNet')
None, 'ResNet'
Return:
scope (str, None): The first scope.
key (str): The remaining key.
"""
split_index = key.find('.')
if split_index != -1:
return key[:split_index], key[split_index + 1:]
else:
return None, key
@property
def name(self):
return self._name
@property
def scope(self):
return self._scope
@property
def module_dict(self):
return self._module_dict
@property
def children(self):
return self._children
def get(self, key):
"""Get the registry record.
Args:
key (str): The class name in string format.
Returns:
class: The corresponding class.
"""
scope, real_key = self.split_scope_key(key)
if scope is None or scope == self._scope:
# get from self
if real_key in self._module_dict:
return self._module_dict[real_key]
else:
# get from self._children
if scope in self._children:
return self._children[scope].get(real_key)
else:
# goto root
parent = self.parent
while parent.parent is not None:
parent = parent.parent
return parent.get(key)
def build(self, *args, **kwargs):
return self.build_func(*args, **kwargs, registry=self)
def _add_children(self, registry):
"""Add children for a registry.
The ``registry`` will be added as children based on its scope.
The parent registry could build objects from children registry.
Example:
>>> models = Registry('models')
>>> mmdet_models = Registry('models', parent=models)
>>> @mmdet_models.register_module()
>>> class ResNet:
>>> pass
>>> resnet = models.build(dict(type='mmdet.ResNet'))
"""
assert isinstance(registry, Registry)
assert registry.scope is not None
assert registry.scope not in self.children, \
f'scope {registry.scope} exists in {self.name} registry'
self.children[registry.scope] = registry
def _register_module(self, module_class, module_name=None, force=False):
if not inspect.isclass(module_class):
raise TypeError('module must be a class, '
f'but got {type(module_class)}')
if module_name is None:
module_name = module_class.__name__
if isinstance(module_name, str):
module_name = [module_name]
for name in module_name:
if not force and name in self._module_dict:
raise KeyError(f'{name} is already registered '
f'in {self.name}')
self._module_dict[name] = module_class
def deprecated_register_module(self, cls=None, force=False):
warnings.warn(
'The old API of register_module(module, force=False) '
'is deprecated and will be removed, please use the new API '
'register_module(name=None, force=False, module=None) instead.')
if cls is None:
return partial(self.deprecated_register_module, force=force)
self._register_module(cls, force=force)
return cls
def register_module(self, name=None, force=False, module=None):
"""Register a module.
A record will be added to `self._module_dict`, whose key is the class
name or the specified name, and value is the class itself.
It can be used as a decorator or a normal function.
Example:
>>> backbones = Registry('backbone')
>>> @backbones.register_module()
>>> class ResNet:
>>> pass
>>> backbones = Registry('backbone')
>>> @backbones.register_module(name='mnet')
>>> class MobileNet:
>>> pass
>>> backbones = Registry('backbone')
>>> class ResNet:
>>> pass
>>> backbones.register_module(ResNet)
Args:
name (str | None): The module name to be registered. If not
specified, the class name will be used.
force (bool, optional): Whether to override an existing class with
the same name. Default: False.
module (type): Module class to be registered.
"""
if not isinstance(force, bool):
raise TypeError(f'force must be a boolean, but got {type(force)}')
# NOTE: This is a walkaround to be compatible with the old api,
# while it may introduce unexpected bugs.
if isinstance(name, type):
return self.deprecated_register_module(name, force=force)
# raise the error ahead of time
if not (name is None or isinstance(name, str) or is_seq_of(name, str)):
raise TypeError(
'name must be either of None, an instance of str or a sequence'
f' of str, but got {type(name)}')
# use it as a normal method: x.register_module(module=SomeClass)
if module is not None:
self._register_module(
module_class=module, module_name=name, force=force)
return module
# use it as a decorator: @x.register_module()
def _register(cls):
self._register_module(
module_class=cls, module_name=name, force=force)
return cls
return _register
第三行无非是初始化Registry类，然后确定其self.build_func = parent.build_func以及parent._add_children(self)。而这里的parent又是Registry('model', build_func=build_model_from_cfg)，也就是将MODELS = Registry('models', parent=MMCV_MODELS)翻译为MODELS = Registry('models', parent=Registry('model', build_func=build_model_from_cfg))
而
def build_backbone(cfg):
"""Build backbone."""
return BACKBONES.build(cfg)
也就对应Registry('models', parent=Registry('model', build_func=build_model_from_cfg)).build_model_from_cfg(cfg)。这里我们以yolo的configs为例来进行讲解。------未完待续