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How do I write function to test if a graph is apex?

I am working on topological graph theory problems and using SageMath. I want to create a function that give a boolean True or False answer, so I can use this answer for further use. My current function that I use:

def is_apex(a):
for v in a.vertex_iterator():
    l=a.neighbors(v)
    if a.is_planar(a.delete_vertex(v)):
        print("Deleting vertex ",v," makes a planar graph")
        a.add_vertex(v)
        a.add_edges([(v, y) for y in l])
    else:
        a.add_vertex(v)
        a.add_edges([(v, y) for y in l])
        print("Deleting vertex ",v," does not make a planar graph")

I am a noob when it comes to programming, and any help would be awesome.

I want a True returned if the graph is apex and a False value to return for not apex.

Thoughts?