Pygraphviz Short Tutorial
-------------------------

See the examples for sample usage and ideas
https://networkx.lanl.gov/browser/pygraphviz/trunk/doc/examples/

There is a complete reference guide at 
https://networkx.lanl.gov/reference/pygraphviz/

The API is very similar to that of NetworkX.  Most of the 
NetworkX tutorial at https://networkx.lanl.gov/wiki/Tutorial 
is applicable to pygraphviz.  See the API notes
https://networkx.lanl.gov/wiki/pygraphviz/API/ for major differences.

Start-up
--------

Import pygraphviz with

>>> import pygraphviz

or to bring into the current namespace without the pygraphviz prefix

>>> from pygraphviz import *


Graphs
------

To make an empty pygraphviz graph use the AGraph class:

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

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

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


Other options for intializing a graph are

using a string,

>>> l=open("ER.dot").readlines() # read file as list 
>>> s=' '.join(l) # make a string by joining list
>>> G=AGraph(s)

using a dict of dicts,

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

or using a SWIG pointer to the AGraph datastructure,

>>> h=AGraph.handle
>>> C=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=AGraph(ranksep='0.1')

Individual node and edge attributes can be set through their attr
dictionary 

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


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

Attributes can be added when adding nodes or edges

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


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()
>>> print s

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