code: def forward(self, x):
      y = self.norm1(x)
      if self.window_size is not None:
          y, pad_hw, num_hw = window_partition(y, self.window_size)
      y = self.attn(y)
      if self.gamma_1 is not None:
          y = self.gamma_1 * y
  
      if self.window_size is not None:
          y = window_unpartition(
              y, pad_hw, num_hw, (x.shape[1], x.shape[2])
          )
      x = x + self.drop_path(y)
      if self.gamma_2 is None:
          x = x + self.drop_path(self.mlp(self.norm2(x)))
      else:
          x = x + self.drop_path(self.gamma_2 * self.mlp(self.norm2(x)))
  
      return x
  
imports: import paddle
  import paddle.nn
  import paddle.nn.functional
  import numpy
  import math
  from paddle import ParamAttr
  from paddle.regularizer import L2Decay
  from paddle.nn.initializer import Constant, TruncatedNormal
  from ppdet.modeling.shape_spec import ShapeSpec
  from ppdet.core.workspace import register, serializable
  from .transformer_utils import zeros_, DropPath, Identity, window_partition, window_unpartition
  from ..initializer import linear_init_
label_desc: Use image node_id 2 for calling the Block obj's underlying member method code with example usage: obj.forward(x) and returns: x