This is a small script which can be used to filter a DOT-language (Graphviz) graph file describing a DAG.

dotfilter.py

import sys
import argparse

import networkx
# pydot is also required


if __name__ == '__main__':
    parser = argparse.ArgumentParser(description='Tool for filtering Graphviz/DOT directed graphs. Pass the source graph on STDIN, the filtered graph will be sent to STDOUT.')
    parser.add_argument('nodes', metavar='node', nargs='+', help='One or more nodes to use for filtering, according to the chosen mode')
    parser.add_argument('--mode', choices=['source','target','through'], default='through', help='Output only that part of the graph that flows out from (source), into (target), or through the specified nodes')
    args = parser.parse_args()
    ##########################

    input_graph = networkx.nx_pydot.read_dot(sys.stdin)

    selected = set()
    for node in args.nodes:
        selected.add(node)
        
        if args.mode in ('source','through'):
            selected = selected.union(networkx.descendants(input_graph, node))

        if args.mode in ('target','through'):
            selected = selected.union(networkx.ancestors(input_graph, node))

    filtered_graph = input_graph.subgraph(selected)

    networkx.nx_pydot.write_dot(filtered_graph, sys.stdout)