old_contents: from .client import APIClient
  
  __all__ = ['APIClient']
  
new_contents: from .client import APIClient
  from pkgutil import extend_path
  
  # Allow out-of-tree submodules.
  __path__ = extend_path(__path__, __name__)
  __all__ = ['APIClient']
  
subject: Allow out-of-tree submodules.