code: def get_bases(definition_dict, loader):
      
      bases = definition_dict.get('bases', ())
      if bases:
          bases = (loader.get_comp_dict(required_version=SPEC_VERSION_TUPLE[0],
                                        **b)
                   for b in bases)
          return SimpleChainmap(definition_dict, *bases)
      else:
          return definition_dict
docs: Collect dependencies.