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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def process_pc_pathsfromto(source_genes, target_genes, neighbor_limit=1, database_filter=None):
 """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. """

    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)