class_docstr: Video 3D stem module. Provides stem operations of Conv, BN, ReLU, MaxPool
  on input data tensor for one or multiple pathways.
code: def _construct_stem(self, dim_in, dim_out):
      assert isinstance(dim_in, Sequence)
      assert all(dim > 0 for dim in dim_in)
      assert isinstance(dim_out, Sequence)
      assert all(dim > 0 for dim in dim_out)
  
      self.blocks = {}
      for p in range(len(dim_in)):
          stem = ResNeXt3DStemSinglePathway(
              dim_in[p],
              dim_out[p],
              self.kernel[p],
              self.stride[p],
              self.padding[p],
              inplace_relu=self.inplace_relu,
              bn_eps=self.bn_eps,
              bn_mmt=self.bn_mmt,
              maxpool=self.maxpool[p],
          )
          stem_name = self._stem_name(p)
          self.add_module(stem_name, stem)
          self.blocks[stem_name] = stem
  
imports: from typing import Sequence
  import torch.nn
  from .r2plus1_util import r2plus1_unit
label_desc: Use image node_id 2 for calling the ResNeXt3DStemMultiPathway obj's underlying member method code with example usage: obj._construct_stem(dim_in, dim_out) without return types