PyGraphviz

# Tutorial

The API is very similar to that of NetworkX. Much of the NetworkX tutorial at http://networkx.github.io/documentation/latest/tutorial/ is applicable to PyGraphviz. See http://pygraphviz.github.io/documentation/latest/reference/api_notes.html for major differences.

## Start-up

Import PyGraphviz with

    >>> import pygraphviz as pgv

or to bring into the current namespace without the “pgv” prefix

    >>> from pygraphviz import *

## Graphs

To make an empty pygraphviz graph use the AGraph class:

    >>> G=pgv.AGraph()

You can use the strict and directed keywords to control what type of graph you want. The default is to create a strict graph (no parallel edges or self-loops). To create a digraph with possible parallel edges and self-loops use

    >>> G=pgv.AGraph(strict=False,directed=True)

You may specify a dot format file to be read on initialization:

    >>> G=pgv.AGraph("Petersen.dot")

Other options for intializing a graph are using a string,

    >>> G=pgv.AGraph('graph {1 - 2}')

using a dict of dicts,

    >>> d={'1': {'2': None}, '2': {'1': None, '3': None}, '3': {'2': None}}
    >>> A=pgv.AGraph(d)

or using a SWIG pointer to the AGraph datastructure,

    >>> h=A.handle
    >>> C=pgv.AGraph(h)

## Nodes, and edges

Nodes and edges can be added one at a time

    >>> G.add_node('a') # adds node 'a'
    >>> G.add_edge('b','c') # adds edge 'b'-'c' (and also nodes 'b', 'c')

or from lists or containers.

    >>> nodelist=['f','g','h']
    >>> G.add_nodes_from(nodelist)

If the node is not a string an attempt will be made to convert it to a string

    >>> G.add_node(1)  # adds node '1'

## Attributes

To set the default attributes for graphs, nodes, and edges use the graph_attr, node_attr, and edge_attr dictionaries

    >>> G.graph_attr['label']='Name of graph'
    >>> G.node_attr['shape']='circle'
    >>> G.edge_attr['color']='red'

Graph attributes can be set when initializing the graph

    >>> G=pgv.AGraph(ranksep='0.1')

Attributes can be added when adding nodes or edges,

    >>> G.add_node(1, color='red')
    >>> G.add_edge('b','c',color='blue')

or through the node or edge attr dictionaries,

    >>> n=G.get_node(1)
    >>> n.attr['shape']='box'

    >>> e=G.get_edge('b','c')
    >>> e.attr['color']='green'

## Layout and Drawing

Pygraphviz provides several methods for layout and drawing of graphs.

To store and print the graph in dot format as a Python string use

    >>> s=G.string()

To write to a file use

    >>> G.write("file.dot")

To add positions to the nodes with a Graphviz layout algorithm

    >>> G.layout() # default to neato
    >>> G.layout(prog='dot') # use dot

To render the graph to an image

    >>> G.draw('file.png')  # write previously positioned graph to PNG file
    >>> G.draw('file.ps',prog='circo') # use circo to position, write PS file