code: def _set_defaults(self):
          
  
          # Register an "enabled" flag on all satchels.
          # How this flag is interpreted depends on the individual satchel.
          _prefix = '%s_enabled' % self.name
          if _prefix not in env:
              env[_prefix] = True
  
          # Do a one-time init of custom defaults.
          _key = '_%s' % self.name
          if _key not in env:
              env[_key] = True
              self.set_defaults()
docs: Wrapper around the overrideable set_defaults().