code: def load_sbml(filename):
      
      import libsbml
  
      document = libsbml.readSBML(filename)
      document.validateSBML()
      num_errors = (document.getNumErrors(libsbml.LIBSBML_SEV_ERROR)
                    + document.getNumErrors(libsbml.LIBSBML_SEV_FATAL))
      if num_errors > 0:
          messages = "The generated document is not valid."
          messages += " {} errors were found:\n".format(num_errors)
          for i in range(document.getNumErrors(libsbml.LIBSBML_SEV_ERROR)):
              err = document.getErrorWithSeverity(i, libsbml.LIBSBML_SEV_ERROR)
              messages += "{}: {}\n".format(err.getSeverityAsString(), err.getShortMessage())
          for i in range(document.getNumErrors(libsbml.LIBSBML_SEV_FATAL)):
              err = document.getErrorWithSeverity(i, libsbml.LIBSBML_SEV_FATAL)
              messages += "{}: {}\n".format(err.getSeverityAsString(), err.getShortMessage())
          raise RuntimeError(messages)
      return import_sbml(document)
docs: Load a model from a SBML file.
  
      Parameters
      ----------
      filename : str
          The input SBML filename.
  
      Returns
      -------
      model : NetworkModel
      y0 : dict
          Initial condition.
      volume : Real or Real3, optional
          A size of the simulation volume.