def addVertices(self, list_vertices=[]):
"""
Add new vertices in the Graph if names are not used
Optional parameters:
list_vertices : a list of names for new vertices
"""
existing_vertices = self.getVertices()
for vertex in list_vertices:
if type(vertex) == str:
if not (vertex in existing_vertices):
newVertex = Vertices(vertex)
self.vertices.append(newVertex)
else:
print("Error : " + vertex + " already exists.")
else:
print("Error : " + vertex + " must be a String.")
