code: def register(self, settings_class=NoSwitcher, *simple_checks,
                   **conditions):
          if settings_class is NoSwitcher:
              def decorator(cls):
                  self.register(cls, *simple_checks, **conditions)
                  return cls
              return decorator
          available_checks = self.checks.keys()
          for condition in conditions.keys():
              if condition not in available_checks:
                  raise InvalidCondition(
                      'There is no check for the condition "%s"' % condition)
          self._registry.append((settings_class, simple_checks, conditions))