[NFC] polish colossalai/builder/pipeline.py code style (#951)

colossalai/builder/pipeline.py

@@ -251,9 +251,9 @@ def build_pipeline_model(layers: nn.Sequential, num_chunks: int = 1, verbose: bo
     partitions = partition_uniform(len(layers), pipeline_parallel_size, num_chunks)
     module_list = []
     for start, end in partitions[pipeline_rank]:
-        module_list.append(nn.Sequential(*[nn.Identity() for _ in range(start)],
+        module_list.append(
-                                         *layers[start:end],
+            nn.Sequential(*[nn.Identity() for _ in range(start)], *layers[start:end],
-                                         *[nn.Identity() for _ in range(len(layers) - end)]))
+                          *[nn.Identity() for _ in range(len(layers) - end)]))
     if verbose:
         logger = get_dist_logger()
         logger.info(f'Total {len(layers)} layers', ranks=[0])
@@ -264,4 +264,3 @@ def build_pipeline_model(layers: nn.Sequential, num_chunks: int = 1, verbose: bo
                 log_str += '\n'.join([str(layer) for layer in layers[start:end]]) + '\n'
             logger.info(log_str, ranks=[0])
     return nn.ModuleList(module_list) if len(module_list) > 1 else module_list[0]
-