old_contents: """
  The :mod:`skmultilearn.cluster` module gathers label space clustering methods.
  
  """
  
  from .base import LabelSpaceNetworkClustererBase, LabelCooccurenceGraphBuilder, GraphBuilderBase
  from .graphtool import GraphToolCooccurenceClusterer
  from .igraph import IGraphLabelCooccurenceClusterer
  from .matrix import MatrixLabelSpaceClusterer
  from .networkx import NetworkXLabelCooccurenceClusterer
  from .random import RandomLabelSpaceClusterer
  
  __all__ = ['LabelSpaceNetworkClustererBase',
             'GraphBuilderBase',
             'LabelCooccurenceGraphBuilder',
             'GraphToolCooccurenceClusterer',
             'IGraphLabelCooccurenceClusterer',
             'MatrixLabelSpaceClusterer',
             'NetworkXLabelCooccurenceClusterer',
             'RandomLabelSpaceClusterer']
  
new_contents: """
  The :mod:`skmultilearn.cluster` module gathers label space clustering methods.
  
  """
  
  from .base import LabelSpaceNetworkClustererBase, LabelCooccurenceGraphBuilder, GraphBuilderBase
  from .matrix import MatrixLabelSpaceClusterer
  from .random import RandomLabelSpaceClusterer
  
  __all__ = ['LabelSpaceNetworkClustererBase',
             'GraphBuilderBase',
             'LabelCooccurenceGraphBuilder',
             'MatrixLabelSpaceClusterer',
             'RandomLabelSpaceClusterer']
  
  # graphtool import optional (is GPL-ed, does not work on windows)
  try:
      from .graphtool import GraphToolCooccurenceClusterer
      __all__ += ['GraphToolCooccurenceClusterer']
  except ImportError:
      pass
  
  # python-igraph import optional (is GPL-ed)
  try:
      from .igraph import IGraphLabelCooccurenceClusterer
  
      __all__ += ['IGraphLabelCooccurenceClusterer']
  except ImportError:
      pass
  
  
  # networkx import is optional
  try:
      from .networkx import NetworkXLabelCooccurenceClusterer
      __all__ += ['NetworkXLabelCooccurenceClusterer']
  except ImportError:
      pass
  
subject: make external library imports optional