old_contents: from .maxflow import *
  from .mincost import *
  from .edmondskarp import *
  from .preflowpush import *
  from .shortestaugmentingpath import *
  from .capacityscaling import *
  from .networksimplex import *
  from .utils import build_flow_dict, build_residual_network
  
  
  __all__ = sum([maxflow.__all__,
                  mincost.__all__,
                  edmondskarp.__all__,
                  preflowpush.__all__,
                  shortestaugmentingpath.__all__,
                  capacityscaling.__all__,
                  networksimplex.__all__,
              ], [])
  
new_contents: # this import is used to combine the __all__ varibles.
  from . import (maxflow, mincost, edmondskarp, preflowpush,
          shortestaugmentingpath, capacityscaling, networksimplex)
  
  __all__ = sum([maxflow.__all__,
                  mincost.__all__,
                  edmondskarp.__all__,
                  preflowpush.__all__,
                  shortestaugmentingpath.__all__,
                  capacityscaling.__all__,
                  networksimplex.__all__,
              ], [])
  
  from .maxflow import *
  from .mincost import *
  from .edmondskarp import *
  from .preflowpush import *
  from .shortestaugmentingpath import *
  from .capacityscaling import *
  from .networksimplex import *
  from .utils import build_flow_dict, build_residual_network
  
subject: Make sure __all__ variables loaded in flow __init__.py