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在Python中，hasattr()、getattr()和setattr()是一组内置函数，用于对对象的属性进行操作和查询。这些函数提供了一种方便的方式来检查对象是否具有特定属性，获取属性的值，以及设置属性的值。

1. hasattr

hasattr()函数是一种重要的工具，用于判断对象是否具有指定的属性或方法。

1.1 语法

hasattr(object, name)

• object – 对象。
• name – 字符串，属性名或方法名。
• 如果对象有该属性返回 True，否则返回 False。

1.2 案例

• 案例1

   gs = max(int(self.model.stride.max() if hasattr(self.model, "stride") else 32), 32)  # grid size (max stride)

• 案例2

if not hasattr(model, "names"):model.names = default_class_names()

• 案例3

data = model.args["data"] if hasattr(model, "args") and isinstance(model.args, dict) else ""

if prompts and hasattr(self.predictor, "set_prompts"):  # for SAM-type modelsself.predictor.set_prompts(prompts)

• 案例4

@propertydef names(self):"""Returns class names of the loaded model."""return self.model.names if hasattr(self.model, "names") else None

• 案例5

  def _close_dataloader_mosaic(self):"""Update dataloaders to stop using mosaic augmentation."""if hasattr(self.train_loader.dataset, "mosaic"):self.train_loader.dataset.mosaic = Falseif hasattr(self.train_loader.dataset, "close_mosaic"):LOGGER.info("Closing dataloader mosaic")self.train_loader.dataset.close_mosaic(hyp=self.args)

• 案例6

  names = model.module.names if hasattr(model, "module") else model.names

• 案例7

 if not self.is_fused():for m in self.model.modules():if isinstance(m, (Conv, Conv2, DWConv)) and hasattr(m, "bn"):if isinstance(m, Conv2):m.fuse_convs()m.conv = fuse_conv_and_bn(m.conv, m.bn)  # update convdelattr(m, "bn")  # remove batchnormm.forward = m.forward_fuse  # update forwardif isinstance(m, ConvTranspose) and hasattr(m, "bn"):m.conv_transpose = fuse_deconv_and_bn(m.conv_transpose, m.bn)delattr(m, "bn")  # remove batchnormm.forward = m.forward_fuse  # update forwardif isinstance(m, RepConv):m.fuse_convs()m.forward = m.forward_fuse  # update forwardself.info(verbose=verbose)

• 案例7

name, m = list((model.model if hasattr(model, "model") else model).named_children())[-1]

• 案例8

if not hasattr(model, "stride"):model.stride = torch.tensor([32.0])

• 案例9

 model = model.fuse().eval() if fuse and hasattr(model, "fuse") else model.eval()  # model in eval mode

 if hasattr(self, "nm"):self.__delattr__("nm")if hasattr(self, "bn"):self.__delattr__("bn")if hasattr(self, "id_tensor"):self.__delattr__("id_tensor")

2. getattr

获取object对象的属性的值，如果存在则返回属性值，如果不存在分为两种情况，一种是没有default参数时，会直接报错；给定了default参数，若对象本身没有name属性，则会返回给定的default值；如果给定的属性name是对象的方法，则返回的是函数对象。需要调用函数对象来获得函数的返回值；调用的话就是函数对象后面加括号，如func之于func()

2.1 语法

getattr(object, name[, default])

• object – 对象。
• name – 字符串，对象属性或方法。
• default – 默认返回值，如果不提供该参数，在没有对应属性时，将触发 AttributeError。

2.2 案例

• 案例1

 file = Path(getattr(model, "pt_path", None) or getattr(model, "yaml_file", None) or model.yaml.get("yaml_file", ""))

• 案例2

  nc = getattr(model, "nc", 10)  # number of classes

• 案例3
  本例中，给定的name是一个方法，通过getattr返回一个函数对象，调用的话就是函数对象后面加括号，然后传入相关的函数参数。

 if name in ("Adam", "Adamax", "AdamW", "NAdam", "RAdam"):optimizer = getattr(optim, name, optim.Adam)(g[2], lr=lr, betas=(momentum, 0.999), weight_decay=0.0)elif name == "RMSProp":optimizer = optim.RMSprop(g[2], lr=lr, momentum=momentum)elif name == "SGD":optimizer = optim.SGD(g[2], lr=lr, momentum=momentum, nesterov=True)else:raise NotImplementedError(f"Optimizer '{name}' not found in list of available optimizers "f"[Adam, AdamW, NAdam, RAdam, RMSProp, SGD, auto].""To request support for addition optimizers please visit https://github.com/ultralytics/ultralytics.")

• 案例4

  if getattr(dataset, "rect", False) and shuffle:LOGGER.warning("WARNING ⚠️ 'rect=True' is incompatible with DataLoader shuffle, setting shuffle=False")shuffle = False

3. setattr

setattr() 函数的功能相对比较复杂，它最基础的功能是修改类实例对象中的属性值。其次，它还可以实现为实例对象动态添加属性或者方法, 设置属性值时，该属性不一定是存在。

3.1 语法

setattr(object, name, value)

3.2 案例

• 案例1

r = self.new()
for k in self._keys:v = getattr(self, k)if v is not None:setattr(r, k, getattr(v, fn)(*args, **kwargs))

• 案例2

for k in "imgsz", "batch":  # allow arg updates to reduce memory on resume if crashed due to CUDA OOMif k in overrides:setattr(self.args, k, overrides[k])

• 案例3

def reshape_outputs(model, nc):"""Update a TorchVision classification model to class count 'n' if required."""name, m = list((model.model if hasattr(model, "model") else model).named_children())[-1]  # last moduleif isinstance(m, Classify):  # YOLO Classify() headif m.linear.out_features != nc:m.linear = nn.Linear(m.linear.in_features, nc)elif isinstance(m, nn.Linear):  # ResNet, EfficientNetif m.out_features != nc:setattr(model, name, nn.Linear(m.in_features, nc))

• 案例4
  通过setattr，实现将b的所有属性和方法，copy给a

def copy_attr(a, b, include=(), exclude=()):"""Copies attributes from object 'b' to object 'a', with options to include/exclude certain attributes."""for k, v in b.__dict__.items():if (len(include) and k not in include) or k.startswith("_") or k in exclude:continueelse:setattr(a, k, v)

代码参考：https://github.com/ultralytics/ultralytics