Python can be used with C source compiled as library and for that the single-file-graph layout library is available based on gml4gtk at https://notabug.org/mooigraph/sfgraph

And older version for python is here for 64bits Linux in rhppython.tar.gz

This is how python can be used for graph layout and sfg.c

# demo program to run sfg layout using python
# first run make swigpython to create the _sfg.so file

import sfg

# get the version number of sfg.c
version=sfg.sfg_version()

print("sfg.c version number is " + str(version));

# all routines return status <0 at error
# and the error codes are in sfg.h found

# first do init
status=sfg.sfg_init();

# a parser must first add all nodes then edges
# node and edge numbers must start with 1 and increase by 1

# add node 1,2 and 3 with size (20,10)
status=sfg.sfg_addnode(1,20,10);
status=sfg.sfg_addnode(2,20,10);
status=sfg.sfg_addnode(3,20,10);

# add edge 1 and 2 from node 1 to 2 and 1 to 3
# the last two numbers are optional size of edgelabel or 0 if no edgelabel
status=sfg.sfg_addedge(1,1,2,0,0);
status=sfg.sfg_addedge(2,1,3,0,0);

# run sugiyama barycenter layout
status=sfg.sfg_layout();

# get lowest and higest node number in use after layout */
nodemin=sfg.sfg_nodemin();
nodemax=sfg.sfg_nodemax();

print("node numbers are in range " + str(nodemin) + " ... " + str(nodemax));

# sfgdmo.c is using a callback routine in c to get the data
# this is manaul getting the node and edge data

for nn in range (nodemin, nodemax+1):
	xpos=sfg.sfg_nodexpos(nn);
	ypos=sfg.sfg_nodeypos(nn);
	print("node " + str(nn) + " is at position (" + str(xpos) +"," + str(ypos) + ")");

# get lowest and higest edge number in use after layout */
edgemin=sfg.sfg_edgemin();
edgemax=sfg.sfg_edgemax();

print("edge numbers are in range " + str(edgemin) + " ... " + str(edgemax));

for ne in range (edgemin, edgemax+1):
	fn=sfg.sfg_edgefrom(ne);
	tn=sfg.sfg_edgeto(ne);
	print("edge "+ str(ne) + " is between node " + str(fn) + " and node " + str(tn));

# sfgdemo.c has example how to create svg image date
# gml4gtk has in main.c example how to using cairo lib
print("and here is the svg image data");

width=sfg.sfg_maxx() + 1;
height=sfg.sfg_maxy() + 5;

print("<svg width=\"" + str(width) + "\" height=\"" + str(height) + "\" xmlns=\"http://www.w3.org/2000/svg\" xmlns:svg=\"http://www.w3.org/2000/svg\">");
print(" <g>");
print("  <title>sfgdemo.py</title>");
print("  <style>");
print("    .small { font: italic 15px sans-serif; }");
print("  </style>");

# get lowest and higest node number in use after layout */
nodemin=sfg.sfg_nodemin();
nodemax=sfg.sfg_nodemax();

for nn in range (nodemin, nodemax+1):
		tx=sfg.sfg_nodexsize(nn);
		ty=sfg.sfg_nodeysize(nn);
		xpos=sfg.sfg_nodexpos(nn);
		ypos=sfg.sfg_nodeypos(nn);
		print("  <rect id=\"node_" + str(nn) + "\" height=\"" + str(ty) + "\" width=\"" + str(tx) + "\" y=\"" + str(ypos) + "\" x=\"" + str(xpos) + "\" stroke-linecap=\"null\" stroke-linejoin=\"null\" stroke-dasharray=\"null\" stroke=\"#000000\" fill=\"#7fff00\"/>");

# get lowest and higest edge number in use after layout */
edgemin=sfg.sfg_edgemin();
edgemax=sfg.sfg_edgemax();

for ne in range (edgemin, edgemax+1):
	rev=sfg.sfg_edgerev(ne);
	scolor = "#000000";
	if (rev == 1):
		scolor = "#0f0fff";
	fn=sfg.sfg_edgefrom(ne);
	tn=sfg.sfg_edgeto(ne);
	typef=sfg.sfg_nodetype(fn);
	typet=sfg.sfg_nodetype(tn);
	fx=sfg.sfg_nodexpos(fn);
	fy=sfg.sfg_nodeypos(fn);
	tx=sfg.sfg_nodexpos(tn);
	ty=sfg.sfg_nodeypos(tn);
	szxf=sfg.sfg_nodexsize(fn);
	szyf=sfg.sfg_nodeysize(fn);
	szxt=sfg.sfg_nodexsize(tn);
	szyt=sfg.sfg_nodeysize(tn);
	if (typef == 1):
		fx = fx + (szxf / 2);
		fy = fy + szyf;
	if (typet == 1):
		tx = tx + (szxt / 2);
	print("  <line id=\"edge_" + str(ne) + "\" y2=\"" + str(ty) + "\" x2=\"" + str(tx) + "\" y1=\"" + str(fy) + "\" x1=\"" + str(fx) + "\" stroke-linecap=\"null\" stroke-linejoin=\"null\" stroke-dasharray=\"null\" stroke-width=\"2\" stroke=\"" + scolor + "\" fill=\"none\"/>");

print(" </g>");
print("</svg>");

# final do de-init and all memory is free()'d
status=sfg.sfg_deinit();

See also for screenshots sfg project