code: def forward(
      self,
      src,
      spatial_shapes,
      level_start_index,
      valid_ratios,
      pos=None,
      padding_mask=None,
  ):
      output = src
      reference_points = self.get_reference_points(
          spatial_shapes, valid_ratios
      )
      for _, layer in enumerate(self.layers):
          output = layer(
              output,
              pos,
              reference_points,
              spatial_shapes,
              level_start_index,
              padding_mask,
          )
  
      return output
  
imports: import copy
  import numpy
  import paddle
  import paddle.nn
  import paddle.nn.functional
  from paddleseg.cvlibs import param_init
  from paddlepanseg.models.param_init import c2_xavier_fill, THLinearInitMixin
  from .common import Conv2D, PositionEmbeddingSine
  from ._ms_deform_attn import MSDeformAttn
label_desc: Use image node_id 3 for calling the MSDeformAttnTransformerEncoder obj's underlying member method code with example usage: obj.forward(src, spatial_shapes, level_start_index, valid_ratios, pos, padding_mask) and returns: output