[NFC] polish colossalai/builder/pipeline.py code style (#638)

colossalai/builder/pipeline.py

 import copy
 import heapq
 
-
 from colossalai.builder import build_model, build_layer
 from colossalai.context.parallel_mode import ParallelMode
 from colossalai.core import global_context as gpc
@@ -40,6 +39,7 @@ def _binary_partition(weights, st, ed):
 def _heap_addition(weights, intervals, add_cnt):
     """
     """
+
     def _heap_push(heap, st, ed):
         value = weights[ed - 1]
         if st > 0:
@@ -162,7 +162,10 @@ def count_layer_params(layers):
     return param_counts
 
 
-def build_pipeline_model_from_cfg(config, num_chunks: int = 1, partition_method: str = 'parameter', verbose: bool = False):
+def build_pipeline_model_from_cfg(config,
+                                  num_chunks: int = 1,
+                                  partition_method: str = 'parameter',
+                                  verbose: bool = False):
     """An initializer to split the model into different stages for pipeline parallelism.
 
     An example for the model config is shown below. The class VisionTransformerFromConfig should
@@ -218,7 +221,7 @@ def build_pipeline_model_from_cfg(config, num_chunks: int = 1, partition_method:
 
             log_str += f'\n===== stage={stage}, layers={num_layers} =====\n'
             for st, ed in parts[stage]:
-                for idx, layer in enumerate(layers[st: ed]):
+                for idx, layer in enumerate(layers[st:ed]):
                     log_str += f'\t{idx + st:2d}: {layer}\n'
         logger.info(log_str, ranks=[0])