[NFC] polish colossalai/engine/schedule/_pipeline_schedule_v2.py code style (#3275)

colossalai/engine/schedule/_pipeline_schedule_v2.py

 #!/usr/bin/env python
 # -*- encoding: utf-8 -*-
 
-from typing import Tuple, Iterable
+from typing import Iterable, Tuple
 
-from colossalai import engine
-import colossalai.communication.p2p_v2 as comm
 import torch.cuda
+
+import colossalai.communication.p2p_v2 as comm
+from colossalai import engine
 from colossalai.context.parallel_mode import ParallelMode
 from colossalai.core import global_context as gpc
 from colossalai.utils.cuda import get_current_device
@@ -35,7 +36,7 @@ def pack_return_tensors(return_tensors):
 class PipelineScheduleV2(PipelineSchedule):
     """Derived class of PipelineSchedule, the only difference is that
        forward_backward_step is reconstructed with p2p_v2
-    
+
     Args:
         num_microbatches (int): The number of microbatches.
         data_process_func (Callable, optional):
@@ -43,9 +44,9 @@ class PipelineScheduleV2(PipelineSchedule):
         tensor_shape (torch.Size, optional): Specified shape in pipeline communication.
         scatter_gather_tensors (bool, optional):
             If set to `True`, communication will be reduced over pipeline when using 1D tensor parallelization.
-    
+
     Example:
-    
+
         # this shows an example of customized data_process_func
         def data_process_func(stage_output, dataloader_output):
             output1, output2 = stage_output