code: def get_neighbor_expression_vector(neighbors, gene_expression_dict):
      
      expressions = []  # Expression vector.
      for gene in neighbors:
          try:
              expression = gene_expression_dict[gene]
          except KeyError:
              continue
  
          expressions.append(expression)
      return expressions
docs: Get an expression vector of neighboring genes.
      Attribute:
          neighbors (list): List of gene identifiers of neighboring genes.
          gene_expression_dict (dict): (Gene identifier)-(gene expression) dictionary.