Neighbors function : problematic

neighbors.py

def find_neighbors(n, v, visited=set()):
    """
    Finds a node's neighbors to n degrees of seperation.

    Param n: degrees of seperation. n > 1
          v: node id

    Return: a list of neighbors to the nth degree with no duplicates or 'NoneType'
    """
    neighbors = set(v.neighbors)
    visited.update([v])
    if n > 1:
        for neighbor in neighbors - visited:
            n_neighbors = find_neighbors(n - 1, neighbor, visited)
            neighbors.update(n_neighbors)
    return neighbors