'''altgraph - a python graph library=================================altgraph is a fork of graphlib.graphlib is a python based graph (network) representation and manipulation package.It has started out as an extension to the C{graph_lib} module written by Nathan DennyU{http://www.ece.arizona.edu/~denny/python_nest/graph_lib_1.0.1.html} but over timeit has been significantly optimized and expanded.The L{Graph} class is loosely modeled after the U{LEDA<http://www.algorithmic-solutions.com/enleda.htm>} (Library of Efficient Datatypes)  representation. The libraryincludes methods for constructing graphs, BFS and DFS traversals,topological sort, finding connected components, shortest paths as well as a numbergraph statistics functions. The library can also visualize graphsvia U{graphviz<http://www.research.att.com/sw/tools/graphviz/>}.The package contains the following modules:    -  the L{Graph} module contains the L{Graph.Graph} class that stores the graph data    -  the L{GraphAlgo} implements graph algorithms operating on graphs (L{Graph.Graph} instances)    -  the L{GraphStat} contains functions for computing statistical measures on graphs    -  the L{GraphUtil} contains functions for generating, reading and saving graphs    -  the L{Dot}  contains functions for displaying graphs via U{graphviz<http://www.research.att.com/sw/tools/graphviz/>}.Download--------Download the  U{python source code<../dist>}.Installation------------Download and unpack the archive then type::    python setup.py installThis will install the library in the default location. For instructions onhow to customize the install procedure read the output of::    python setup.py --help installTo verify the installation procedure switch to the test directory un run thetest_graphib.py file that is located there::    python test_altgraph.pyExample usage-------------Lets assume that we want to analyze the graph below (links to the full picture) GRAPH_IMG.Our script then might look the following way::    from altgraph import Graph, GraphAlgo, Dot    # these are the edges    edges = [ (1,2), (2,4), (1,3), (2,4), (3,4), (4,5), (6,5),    (6,14), (14,15), (6, 15),  (5,7), (7, 8), (7,13), (12,8),    (8,13), (11,12), (11,9), (13,11), (9,13), (13,10) ]    # creates the graph    graph = Graph.Graph()    for head, tail in edges:        graph.add_edge(head, tail)    # do a forward bfs from 1 at most to 20    print graph.forw_bfs(1)This will print the nodes in some breadth first order::    [1, 2, 3, 4, 5, 7, 8, 13, 11, 10, 12, 9]If we wanted to get the hop-distance from node 1 to node 8we coud write::    print graph.get_hops(1, 8)This will print the following::    [(1, 0), (2, 1), (3, 1), (4, 2), (5, 3), (7, 4), (8, 5)]Node 1 is at 0 hops since it is the starting node, nodes 2,3 are 1 hop away ...node 8 is 5 hops away. To find the shortest distance between two nodes youcan use::    print GraphAlgo.shortest_path(graph, 1, 12)It will print the nodes on one (if there are more) the shortest paths::    [1, 2, 4, 5, 7, 13, 11, 12]To display the graph we can use the GraphViz backend::    dot = Dot.Dot(graph)    # display the graph on the monitor    dot.display()    # save it in an image file    dot.save_img(file_name='graph', file_type='gif')@author: U{Istvan Albert<http://www.personal.psu.edu/staff/i/u/iua1/>}@license:  MIT LicenseCopyright (c) 2004 Istvan Albert unless otherwise noted.Permission is hereby granted, free of charge, to any person obtaining a copy of this softwareand associated documentation files (the "Software"), to deal in the Software without restriction,including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense,and/or sell copies of the Software, and to permit persons to whom the Software is furnished to doso.THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULARPURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLEFOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS INTHE SOFTWARE.@requires: Python 2.3 or higher@newfield contributor: Contributors:@contributor: U{Reka Albert <http://www.phys.psu.edu/~ralbert/>}'''__version__ = '0.6.5'class GraphError(ValueError):    pass