Tutorial¶
The API is very similar to that of NetworkX. Much of the NetworkX tutorial at https://networkx.org/documentation/latest/tutorial.html 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
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 initializing 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