code: def process_pc_neighborhood(gene_names, neighbor_limit=1,
                              database_filter=None):
      
      model = pcc.graph_query('neighborhood', gene_names,
                              neighbor_limit=neighbor_limit,
                              database_filter=database_filter)
      if model is not None:
          return process_model(model)
docs: Returns a BiopaxProcessor for a PathwayCommons neighborhood query.
  
      The neighborhood query finds the neighborhood around a set of source genes.
  
      http://www.pathwaycommons.org/pc2/#graph
  
      http://www.pathwaycommons.org/pc2/#graph_kind
  
      Parameters
      ----------
      gene_names : list
          A list of HGNC gene symbols to search the neighborhood of.
          Examples: ['BRAF'], ['BRAF', 'MAP2K1']
      neighbor_limit : Optional[int]
          The number of steps to limit the size of the neighborhood around
          the gene names being queried. Default: 1
      database_filter : Optional[list]
          A list of database identifiers to which the query is restricted.
          Examples: ['reactome'], ['biogrid', 'pid', 'psp']
          If not given, all databases are used in the query. For a full
          list of databases see http://www.pathwaycommons.org/pc2/datasources
  
      Returns
      -------
      bp : BiopaxProcessor
          A BiopaxProcessor containing the obtained BioPAX model in bp.model.