old_contents: from .model_checker import ModelChecker, PathResult, PathMetric, get_path_iter
  from .pysb import PysbModelChecker
  from .signed_graph import SignedGraphModelChecker
  from .unsigned_graph import UnsignedGraphModelChecker
  from .pybel import PybelModelChecker
  
new_contents: from .model_checker import ModelChecker, PathResult, PathMetric, get_path_iter
  from .pysb import PysbModelChecker
  from .signed_graph import SignedGraphModelChecker
  from .unsigned_graph import UnsignedGraphModelChecker
  from .pybel import PybelModelChecker
  from .model_checker import signed_edges_to_signed_nodes, prune_signed_nodes
  
subject: Make function top level importable