Observation.v1

property Observation.v1: Vertex | None

First vertex of the edge, the start vertex for a directed edge

Returns:

the vertex, or None if the edge is not connected

Return type:

Vertex subclass or None

Changed in version 1.0: Read-only. It was a plain attribute, so assigning to it on an edge that was in a graph left the graph inconsistent: the vertices’ edge lists no longer agreed with the edge, and the edge could not be removed. Give the vertices to the constructor, Edge(v1, v2), or to connect or Vertex.connect.

Seealso:

v2 connect