code: def _default_anchorgen():
      anchor_sizes = ((32,), (64,), (128,), (256,), (512,))
      aspect_ratios = ((0.5, 1.0, 2.0),) * len(anchor_sizes)
      return AnchorGenerator(anchor_sizes, aspect_ratios)
  
imports: from typing import Any, Callable, List, Optional, Tuple, Union
  import torch
  import torch.nn.functional
  from torch import nn
  from torchvision.ops import MultiScaleRoIAlign
  from ...ops import misc
  from ...transforms._presets import ObjectDetection
  from .._api import register_model, Weights, WeightsEnum
  from .._meta import _COCO_CATEGORIES
  from .._utils import _ovewrite_value_param, handle_legacy_interface
  from ..mobilenetv3 import mobilenet_v3_large, MobileNet_V3_Large_Weights
  from ..resnet import resnet50, ResNet50_Weights
  from ._utils import overwrite_eps
  from .anchor_utils import AnchorGenerator
  from .backbone_utils import _mobilenet_extractor, _resnet_fpn_extractor, _validate_trainable_layers
  from .generalized_rcnn import GeneralizedRCNN
  from .roi_heads import RoIHeads
  from .rpn import RegionProposalNetwork, RPNHead
  from .transform import GeneralizedRCNNTransform
label_desc: Use image node_id 1 for calling a global function with example usage: _default_anchorgen() and returns: AnchorGenerator