class_docstr: Basic weighted, directed graph class
  
  Member variables:
  
  * V (int): the number of vertices
  * E (int): the number of edges
  
  Methods
  
  * vertices (list, type=int, shape=(V,)): vertices id
  * edges (list, type=int, shape=(E,2)): edges as vertices id tuples
  * weights (list, type=int, shape=(E,)): weights / lengths
    of the graph's edges
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code: def get_weights(self):
      return self.weights
  
imports: import numpy
  from scipy.sparse import coo_matrix
label_desc: Use image node_id 3 for calling the WeightedGraph obj's underlying member method code with example usage: obj.get_weights() and returns: self