new_contents: import warnings
  try:
      import PySide  # noqa
  except ImportError:
      warnings.warn("Failed to import PySide. "
                    "gui will not be available.", ImportWarning)
  
      def main():
          """Start signac-gui.
  
          The gui is only available if PySide is installed."""
          raise ImportError(
              "You need to install PySide to use the gui.")
  else:
      from .gui import main
  
  __all__ = ['main']
  
subject: Add gui/__init__.py