## Introduction

A graph in mathematics and computer science consists of “nodes” which may or may not be connected with one another. Connections between nodes are called edges. A graph can be directed (arrows) or undirected. The edges could represent distance or weight.

Python does not have a graph data type. To use graphs we can either use a module or implement it ourselves:

- implement graphs ourselves
- networkx module

## Graph in Python

A directed graph can be defined as:

#!/usr/bin/env python graph = {'A': ['B', 'C'], 'B': ['C', 'A'], 'C': ['D'], 'D': ['A']} print(graph) |

## Graphs using networkx

The networkx software module has support for creating, manipulating graphs.

#!/usr/bin/env python import networkx as nx G=nx.Graph() G.add_node("A") G.add_node("B") G.add_node("C") G.add_edge("A","B") G.add_edge("B","C") G.add_edge("C","A") print("Nodes: " + str(G.nodes())) print("Edges: " + str(G.edges())) |

Result:

Nodes: ['A', 'C', 'B']

Edges: [('A', 'C'), ('A', 'B'), ('C', 'B')]

Edges: [('A', 'C'), ('A', 'B'), ('C', 'B')]

import networkx as nx

dosen’t work syntaxerror

Install the networkx module using: pip install networkx

You will need to install virtualenv on OSX otherwise you will have trouble installing networkx module.