code: def variants_of(
          graph: BELGraph,
          node: Protein,
          modifications: Optional[Set[str]] = None,
  ) -> Set[Protein]:
      
      if modifications:
          return _get_filtered_variants_of(graph, node, modifications)
  
      return {
          v
          for u, v, key, data in graph.edges(keys=True, data=True)
          if (
              u == node
              and data[RELATION] == HAS_VARIANT
              and pybel.struct.has_protein_modification(v)
          )
      }
docs: Returns all variants of the given node.