https://github.com/bwesterb/py-tarjan

Python implementation of Tarjan's strongly connected components algorithm.
https://github.com/bwesterb/py-tarjan

dependancy-manager graph-algorithms python scc tarjan transitive-closure

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Python implementation of Tarjan's strongly connected components algorithm.

• Host: GitHub
• URL: https://github.com/bwesterb/py-tarjan
• Owner: bwesterb
• License: lgpl-3.0
• Created: 2011-09-05T09:48:58.000Z (over 13 years ago)
• Default Branch: master
• Last Pushed: 2023-04-14T08:37:57.000Z (over 1 year ago)
• Last Synced: 2024-09-21T11:48:25.495Z (3 months ago)
• Topics: dependancy-manager, graph-algorithms, python, scc, tarjan, transitive-closure
• Language: Python
• Homepage:
• Size: 75.2 KB
• Stars: 92
• Watchers: 10
• Forks: 16
• Open Issues: 0
• Metadata Files:
  • Readme: README.rst
  • Changelog: CHANGES.rst
  • License: LICENSE

Awesome Lists containing this project

• awesome-algorithms - py-tarjan - Python implementation of Tarjan's strongly connected components algorithm. (Awesome Algorithms / SCC - Strongly connected component (强连通分量))

README

        
Python implementation of Tarjan's algorithm

===========================================

Tarjan's algorithm takes as input a directed (possibly cyclic!) graph and

returns as output its strongly connected components in a topological order.

Example

-------

.. image:: https://raw.githubusercontent.com/bwesterb/py-tarjan/master/doc/example.png

.. code::

   >>> tarjan({1:[2],2:[1,5],3:[4],4:[3,5],5:[6],6:[7],7:[8],8:[6,9],9:[]})

   [[9], [8, 7, 6], [5], [2, 1], [4, 3]]

Uses

----

Cyclic dependencies

~~~~~~~~~~~~~~~~~~~

In various cases, dependencies might be cyclic and a group of interdependant

actions must be executed simultaneously.  It is not uncommon that

the simulataneous execution is costly.  With Tarjan's algorithm, one can

determine an efficient order in which to execute the groups of interdependant

actions.

Transitive closure

~~~~~~~~~~~~~~~~~~

Using Tarjan's algorithm, one can efficiently compute the transitive

closure of a graph.  (Given a graph *G*, the transitive closure of *G*

is a graph that contains the same vertices and contains an edge from *v*

to *w* if and only if there is a path from *v* to *w* in *G*.)

The transitive closure is implemented in `tarjan.tc`:

.. code::

    >>> from tarjan.tc import tc

    >>> tc({1:[2],2:[1,5],3:[4],4:[3,5],5:[6],6:[7],7:[8],8:[6,9],9:[]})

    {1: (1, 2, 5, 6, 7, 8, 9),

     2: (1, 2, 5, 6, 7, 8, 9),

     3: (3, 4, 5, 6, 7, 8, 9),

     4: (3, 4, 5, 6, 7, 8, 9),

     5: (8, 9, 6, 7),

     6: (8, 9, 6, 7),

     7: (8, 9, 6, 7),

     8: (8, 9, 6, 7),

     9: ()}

Expand group hierarchies

~~~~~~~~~~~~~~~~~~~~~~~~

Given a graph of groups, one can use the transitive closure to determine

all indirect members of a group.  (Someone is an indirect member of a group,

if it is a member of a group that is a member of a group that ... is a member

of the group.)

Installation

------------

Simply execute

.. code::

    pip install tarjan

or from this source distribution, run

.. code::

    python setup.py install

.. image:: https://travis-ci.org/bwesterb/py-tarjan.png

   :target: https://travis-ci.org/bwesterb/py-tarjan