parse multiple digraph in one dot file

I'm trying to process and render some graph in DOT format. The dot file I have is large (~300MB), and it contains multiple digraphs

digraph 1 {...}
digraph 2 {...}
digraph 3 {...}

I ha开发者_如何学Cve got 2 questions:

1. Is it possible to use render only 1 digraph instead of the whole graph?

Something like dot -3 -Tps mygraph.dot -o out.ps to render digraph 3 only?

2.What's the best Python library to process dot format?(other languages are also acceptable)

Here are two I tried, but not good enough

pydot It gives me a digraph list after importing, which is good, but it doesn't handle "." in the node name. For example nd.nd [label="nd_node"] will fail

pygraphviz It does handle ".", but only imports digraph 1 when given multiple graph definition in a file :(

Since you have dot, you should also have gvpr, a graph-processing tool. You can print the third graph with a simple gvpr script, like so:

BEGIN { int count = 0; }
BEG_G {
    count = count + 1;
    if(count == 3) {
        write($G);
    }
}

Then, you can use this as a source filter:

cat mygraph.dot | gvpr -f thirdgraph.gv | dot -Tps -o out.ps

Not sure if this is what you wanted, but you just need to write a simple parser, or whatever you want to call it. The pygraphviz handles file input by simply read and parse as it would for string input.

So, a sample piece of code would be:

f = open(filename, 'r')
graph = [[]]
while True:
    line = f.readline()
    if not line:
        break
    if declare_new_graph(line):
        graph.append([])
    graph[-1].append(line)

#now you have a list of graphs
#each is a list of lines
#with first line containing the name
#to get the string representation of graph "i"
str = '\n'.join(graph[i])