class_docstr: Implements the Mask2Former head.
  
  See `Masked-attention Mask Transformer for Universal Image
  Segmentation <https://arxiv.org/pdf/2112.01527>`_ for details.
  
  Args:
      in_channels (list[int]): Number of channels in the input feature map.
      feat_channels (int): Number of channels for features.
      out_channels (int): Number of channels for output.
      num_things_classes (int): Number of things.
      num_stuff_classes (int): Number of stuff.
      num_queries (int): Number of query in Transformer decoder.
      pixel_decoder (:obj:`ConfigDict` or dict): Config for pixel
          decoder. Defaults to None.
      enforce_decoder_input_project (bool, optional): Whether to add
          a layer to change the embed_dim of tranformer encoder in
          pixel decoder to the embed_dim of transformer decoder.
          Defaults to False.
      transformer_decoder (:obj:`ConfigDict` or dict): Config for
          transformer decoder. Defaults to None.
      positional_encoding (:obj:`ConfigDict` or dict): Config for
          transformer decoder position encoding. Defaults to
          dict(num_feats=128, normalize=True).
      loss_cls (:obj:`ConfigDict` or dict): Config of the classification
          loss. Defaults to None.
      loss_mask (:obj:`ConfigDict` or dict): Config of the mask loss.
          Defaults to None.
      loss_dice (:obj:`ConfigDict` or dict): Config of the dice loss.
          Defaults to None.
      train_cfg (:obj:`ConfigDict` or dict, optional): Training config of
          Mask2Former head.
      test_cfg (:obj:`ConfigDict` or dict, optional): Testing config of
          Mask2Former head.
      init_cfg (:obj:`ConfigDict` or dict or list[:obj:`ConfigDict` or             dict], optional): Initialization config dict. Defaults to None.
docstr: Forward for head part which is called after every decoder layer.
  
  Args:
      decoder_out (Tensor): in shape (batch_size, num_queries, c).
      mask_feature (Tensor): in shape (batch_size, c, h, w).
      attn_mask_target_size (tuple[int, int]): target attention
          mask size.
  
  Returns:
      tuple: A tuple contain three elements.
  
          - cls_pred (Tensor): Classification scores in shape                     (batch_size, num_queries, cls_out_channels).                     Note `cls_out_channels` should includes background.
          - mask_pred (Tensor): Mask scores in shape                     (batch_size, num_queries,h, w).
          - attn_mask (Tensor): Attention mask in shape                     (batch_size * num_heads, num_queries, h, w).
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code: def _forward_head(
      self,
      decoder_out: Tensor,
      mask_feature: Tensor,
      attn_mask_target_size: Tuple[int, int],
  ) -> Tuple[Tensor]:
      """Forward for head part which is called after every decoder layer.
  
          Args:
              decoder_out (Tensor): in shape (batch_size, num_queries, c).
              mask_feature (Tensor): in shape (batch_size, c, h, w).
              attn_mask_target_size (tuple[int, int]): target attention
                  mask size.
  
          Returns:
              tuple: A tuple contain three elements.
  
                  - cls_pred (Tensor): Classification scores in shape \
                      (batch_size, num_queries, cls_out_channels). \
                      Note `cls_out_channels` should includes background.
                  - mask_pred (Tensor): Mask scores in shape \
                      (batch_size, num_queries,h, w).
                  - attn_mask (Tensor): Attention mask in shape \
                      (batch_size * num_heads, num_queries, h, w).
          """
      decoder_out = self.transformer_decoder.post_norm(decoder_out)
      # shape (num_queries, batch_size, c)
      cls_pred = self.cls_embed(decoder_out)
      # shape (num_queries, batch_size, c)
      mask_embed = self.mask_embed(decoder_out)
      # shape (num_queries, batch_size, h, w)
      mask_pred = torch.einsum(
          "bqc,bchw->bqhw", mask_embed, mask_feature
      )
      attn_mask = F.interpolate(
          mask_pred,
          attn_mask_target_size,
          mode="bilinear",
          align_corners=False,
      )
      # shape (num_queries, batch_size, h, w) ->
      #   (batch_size * num_head, num_queries, h, w)
      attn_mask = (
          attn_mask.flatten(2)
          .unsqueeze(1)
          .repeat((1, self.num_heads, 1, 1))
          .flatten(0, 1)
      )
      attn_mask = attn_mask.sigmoid() < 0.5
      attn_mask = attn_mask.detach()
  
      return cls_pred, mask_pred, attn_mask
  
imports: import copy
  from typing import List, Tuple
  import torch
  import torch.nn
  import torch.nn.functional
  from mmcv.cnn import Conv2d
  from mmcv.ops import point_sample
  from mmengine.model import ModuleList, caffe2_xavier_init
  from mmengine.structures import InstanceData
  from torch import Tensor
  from mmdet.registry import MODELS, TASK_UTILS
  from mmdet.structures import SampleList
  from mmdet.utils import ConfigType, OptConfigType, OptMultiConfig, reduce_mean
  from ..layers import Mask2FormerTransformerDecoder, SinePositionalEncoding
  from ..utils import get_uncertain_point_coords_with_randomness
  from .anchor_free_head import AnchorFreeHead
  from .maskformer_head import MaskFormerHead
label_desc: Use image node_id 5 for calling the Mask2FormerHead obj's underlying member method code with example usage: obj._forward_head(decoder_out, mask_feature, attn_mask_target_size) and returns: cls_pred,  mask_pred,  attn_mask