class_docstr: A connected graph of Vertex/Edge objects. A GraphBase is a *component* of a Graph that contains a connected set of Vertex and Edges.
  
  Attributes:
      verticesPoset (Poset[Vertex]): the partially ordered set of vertices of the graph.
      edgesPoset (Poset[Edge]): the partially ordered set of edges of the graph.
      loops (set[Edge]): the set of *loop* edges (of degree 0).
      directed (bool): indicates if the graph is considered *oriented* or not.
class_docstr_tok: ["A","connected","graph","of","Vertex\/Edge","objects",".","A","GraphBase","is","a","*","component","*","of","a","Graph","that","contains","a","connected","set","of","Vertex","and","Edges",".","Attributes",":","verticesPoset","(","Poset","[","Vertex","]",")",":","the","partially","ordered","set","of","vertices","of","the","graph",".","edgesPoset","(","Poset","[","Edge","]",")",":","the","partially","ordered","set","of","edges","of","the","graph",".","loops","(","set","[","Edge","]",")",":","the","set","of","*","loop","*","edges","(","of","degree","0",")",".","directed","(","bool",")",":","indicates","if","the","graph","is","considered","*","oriented","*","or","not","."]
docstr: allow a GraphBase to hold a single vertex.
docstr_tok: ["allow","a","GraphBase","to","hold","a","single","vertex","."]
code: def add_single_vertex(self, v):
      """
      allow a GraphBase to hold a single vertex.
      """
      if len(self.edgesPoset) == 0 and len(self.verticesPoset) == 0:
          v = self.verticesPoset.add(v)
          v.component = self
          return v
      return None
  
imports: from graphistry.layout.utils import Poset
label_desc: Use image node_id 4 for calling the GraphBase obj's underlying member method code with example usage: obj.add_single_vertex(v) and returns: None, v