code: def process_pc_pathsfromto(source_genes, target_genes, neighbor_limit=1,
                             database_filter=None):
      
      model = pcc.graph_query('pathsfromto', source_genes,
                               target_genes, neighbor_limit=neighbor_limit,
                               database_filter=database_filter)
      if model is not None:
          return process_model(model)
docs: Returns a BiopaxProcessor for a PathwayCommons paths-from-to query.
  
      The paths-from-to query finds the paths from a set of source genes to
      a set of target genes.
  
      http://www.pathwaycommons.org/pc2/#graph
  
      http://www.pathwaycommons.org/pc2/#graph_kind
  
      Parameters
      ----------
      source_genes : list
          A list of HGNC gene symbols that are the sources of paths being
          searched for.
          Examples: ['BRAF', 'RAF1', 'ARAF']
      target_genes : list
          A list of HGNC gene symbols that are the targets of paths being
          searched for.
          Examples: ['MAP2K1', 'MAP2K2']
      neighbor_limit : Optional[int]
          The number of steps to limit the length of the paths
          between the source genes and target genes 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.