abstract 2019.12.29

Python library for creating and drawing graphs and taking advantage of graph properties

Abstract

Abstract is a Python library for creating and drawing graphs and taking advantage of graph properties.

Installation

pip install abstract

or

pip install git+https://github.com/idin/abstract.git

Graph

Introduction

In computer science, a graph is an abstract data type that is meant to implement the undirected graph and directed graph concepts from mathematics; specifically, the field of graph theory. [1]

A graph data structure consists of a finite (and possibly mutable) set of vertices or nodes or points, together with a set of unordered pairs of these vertices for an undirected graph or a set of ordered pairs for a directed graph. These pairs are known as edges, arcs, or lines for an undirected graph and as arrows, directed edges, directed arcs, or directed lines for a directed graph. The vertices may be part of the graph structure, or may be external entities represented by integer indices or references. [1]

Usage

The Graph class allows you to create nodes and edges and visualize the resulting graph. Edges can have direction which indicates parent-child relationship.

To construct a new graph, use Graph().

from abstract import Graph

graph = Graph()

add_node

The add_node method creates a node in the graph and returns a Node object.

It takes the following arguments:

• name: name of the new node (should be unique); snake case is recommended
• label (optional): it can be any string, if it is missing the name will be displayed
• value (optional): can be any object
• style (optional): it should be a NodeStyle object and is only used for rendering
• if_node_exists: what to do if a node with this name exists and can be 'warn', 'error', or 'ignore'; default is 'warn'

node_order = [
    'scissors', 'paper', 'rock', 'lizard', 'Spock', 'scissors',
    'lizard', 'paper', 'Spock', 'rock', 'scissors'
]

# add nodes (avoid duplicates)
for node in set(node_order):
    node = graph.add_node(name=node)

connect (add an edge)

The connect method creates an edge from a start node to an end node. The start and end arguments can be either names of nodes or the Node objects.

for index in range(len(node_order)-1):
    edge = graph.connect(start=node_order[index], end=node_order[index+1])

get_node

To retrieve a node from the graph you can use the get_node method which returns a Node object.

rock = graph.get_node('rock')

draw (render)

The render method visualizes the graph and if a path is provided it saves it to an image file that can be a pdf or png. The file format is infered from the path argument. The draw method is just an alias for render.

# just visualize the graph
graph.draw()

# save as a png file and view the file
graph.draw(path='my_graph.png', view=True)

Graph(obj)

You can create a graph from any object that has a "__graph__()" method. Examples of such objects are:

• Graph class from this library
• Pensieve class from the pensieve library

from pensieve import Pensieve
from abstract import Graph

pensieve = Pensieve()
pensieve['one'] = 1
pensieve['two'] = 2
pensieve.store(key='three', precursors=['one', 'two'], function=lambda x: x['one'] + x['two'])
graph = Graph(pensieve)

draw_graph

In case you just want to draw the graph of an object or create a graph and immediately render it you can just use the draw_graph method. It accepts anything that the Graph class accepts.

from pensieve import Pensieve
from abstract import draw_graph

pensieve = Pensieve()
pensieve['one'] = 1
pensieve['two'] = 2
pensieve.store(key='three', precursors=['one', 'two'], function=lambda x: x['one'] + x['two'])
draw_graph(pensieve)

Future Features

• Create a graph from:
  • list of dictionaries
  • dataframe
• Create a new graph by filtering a graph