Set node positions using Graphviz in Jupyter Python

Question

I want to make a graph with random node positions but it seems that the "pos" attribute for nodes does nothing. Here is a minimal example:

import graphviz
import pylab
from graphviz import Digraph

g = Digraph('G', filename='ex.gv',format='pdf')
g.attr(size='7')
g.node('1',pos='1,2')
g.node('2',pos='2,3')
g.node('3',pos='0,0')
g.edge('1','2')
g.edge('1','3')
graphviz.Source(g)

Any ideas of how achieve that? Thanks in advance.

Answer 1

Although not 100% clear in the docs, I think pos is not supported in the dot engine on input. The fdp or neato engines do support pos on input for setting the initial position, and if you end the coordinate specification with '!', the coordinates will not change and thus become the final node position.

Play with a live example at https://beta.observablehq.com/@magjac/placing-graphviz-nodes-in-fixed-positions

This standalone python script generates a pdf with the expected node positions:

#!/usr/bin/python

import graphviz
from graphviz import Digraph

g = Digraph('G', engine="neato", filename='ex.gv',format='pdf')
g.attr(size='7')
g.node('1',pos='1,2!')
g.node('2',pos='2,3!')
g.node('3',pos='0,0!')
g.edge('1','2')
g.edge('1','3')
g.render()

Since SO does not support pdf uploading, here's a png image generated with the same code except format='png':

Without the exclamation marks you get:

Without any pos attributes at all you get a similar (but not exactly the same) result: