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networkx::base Namespace Reference


Detailed Description

Base classes for graphs and digraphs.

Unless otherwise specified, by graph we mean a simple graph that has
no self-loops or multiple (parallel) edges. (See the module xbase.py
for graph classes XGraph and XDiGraph that allow for self-loops,
mutiple edges and arbitrary objects associated with edges.)

The following classes are provided:

Graph
   The basic operations common to graph-like classes.

DiGraph
   Operations common to digraphs, a graph with directed edges.
   Subclass of Graph.

An empty graph or digraph is created with
 - G=Graph()
 - G=DiGraph()

This module implements graphs using data structures based on an
adjacency list implemented as a node-centric dictionary of
dictionaries. The dictionary contains keys corresponding to the nodes
and the values are dictionaries of neighboring node keys with the
value None (the Python None type).  This allows fast addition,
deletion and lookup of nodes and neighbors in large graphs.  The
underlying datastructure should only be visible in this module. In all
other modules, instances of graph-like objects are manipulated solely
via the methods defined here and not by acting directly on the
datastructure.

The following notation is used throughout NetworkX documentation and
code: (we use mathematical notation n,v,w,... to indicate a node,
v=vertex=node).
 
G,G1,G2,H,etc:
   Graphs

n,n1,n2,u,v,v1,v2:
   nodes (v stands for vertex=node)

nlist,vlist:
   a list of nodes 

nbunch:
   a "bunch" of nodes (vertices).  An nbunch is any iterable container
   of nodes that is not itself a node in the graph. (It can be an
   iterable or an iterator, e.g. a list, set, graph, file, etc..)
   
e=(n1,n2):
   an edge (a python "2-tuple") in the Graph and DiGraph classes,
   also written n1-n2 (if undirected), or n1->n2 (if directed).
   Note that 3-tuple edges of the form (n1,n2,x) are used in the
   XGraph and XDiGraph classes. See xbase.py for details on how
   2-tuple edges, such as (n1,n2), are translated when 3-tuple edges
   are expected. For example, if G is an XGraph, then G.add_edge(n1,n2)
   will add the edge (n1,n2,None), and G.delete_edge(n1,n2) will attempt
   to delete the edge (n1,n2,None). In the case of multiple edges between
   nodes n1 and n2, one can use G.delete_multiedge(n1,n2) to delete all
   edges between n1 and n2.

elist:
   a list of edges (as tuples)

ebunch:
   a bunch of edges (as tuples)
   an ebunch is any iterable (non-string) container
   of edge-tuples. (Similar to nbunch, also see add_edge).

Warning:
  - The ordering of objects within an arbitrary nbunch/ebunch
    can be machine- or implementation-dependent.
  - Algorithms should treat an arbitrary nbunch/ebunch as
    once-through-and-exhausted iterable containers.
  - len(nbunch) and len(ebunch) need not be defined.    


Methods
=======

The Graph class provides rudimentary graph operations:

Mutating Graph methods
----------------------
   
    - G.add_node(n), G.add_nodes_from(nbunch)
    - G.delete_node(n), G.delete_nodes_from(nbunch)
    - G.add_edge(n1,n2), G.add_edge(e), where e=(u,v)
    - G.add_edges_from(ebunch)
    - G.delete_edge(n1,n2), G.delete_edge(e), where e=(u,v)
    - G.delete_edges_from(ebunch)
    - G.add_path(nlist)
    - G.add_cycle(nlist)
    - G.clear()
    - G.subgraph(nbunch,inplace=True)

Non-mutating Graph methods
--------------------------

    - len(G)
    - n in G (equivalent to G.has_node(n))
    - G.has_node(n)
    - G.nodes()
    - G.nodes_iter()
    - G.has_edge(n1,n2)
    - G.edges(), G.edges(n), G.edges(nbunch)      
    - G.edges_iter(), G.edges_iter(n), G.edges_iter(nbunch)
    - G.neighbors(n)
    - G[n]  (equivalent to G.neighbors(n))
    - G.neighbors_iter(n) # iterator over neighbors
    - G.number_of_nodes()
    - G.number_of_edges()
    - G.degree(n), G.degree(nbunch)
    - G.degree_iter(n), G.degree_iter(nbunch)
    - G.is_directed()

Methods returning a new graph
-----------------------------

    - G.subgraph(nbunch)
    - G.subgraph(nbunch,create_using=H)
    - G.copy()
    - G.to_undirected()
    - G.to_directed()
    
Examples
========

Create an empty graph structure (a "null graph") with
zero nodes and zero edges.

>>> from networkx import *
>>> G=Graph()

G can be grown in several ways.
By adding one node at a time:

>>> G.add_node(1)

by adding a list of nodes:

>>> G.add_nodes_from([2,3])

by using an iterator:

>>> G.add_nodes_from(xrange(100,110))

or by adding any nbunch of nodes (see above definition of an nbunch):

>>> H=path_graph(10)
>>> G.add_nodes_from(H)

H can be another graph, or dict, or set, or even a file.
Any hashable object (except None) can represent a node, e.g. a Graph,
a customized node object, etc.

>>> G.add_node(H)

G can also be grown by adding one edge at a time:

>>> G.add_edge( (1,2) )

by adding a list of edges: 

>>> G.add_edges_from([(1,2),(1,3)])

or by adding any ebunch of edges (see above definition of an ebunch):

>>> G.add_edges_from(H.edges())

There are no complaints when adding existing nodes or edges:

>>> G=Graph()
>>> G.add_edge([(1,2),(1,3)])

will add new nodes as required.
    


Classes

class  DiGraph
class  Graph
class  NetworkXError
class  NetworkXException

Functions

def _test_suite
def degree
def degree_histogram
def density
def edges
def edges_iter
def is_directed
def neighbors
def nodes
def nodes_iter
def number_of_edges
def number_of_nodes

Variables

string __author__ = """Aric Hagberg (hagberg@lanl.gov)\nPieter Swart (swart@lanl.gov)\nDan Schult(dschult@colgate.edu)"""
string __credits__ = """"""
string __date__ = "$Date: 2005-06-24 14:16:40 -0600 (Fri, 24 Jun 2005) $"
string __revision__ = "$Revision: 1061 $"
list nxbase = sys.path[0]


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