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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") # doctest: +SKIP
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
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