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<a href="CedarBackup2-module.html">Package CedarBackup2</a> ::
<a href="CedarBackup2.util-module.html">Module util</a> ::
Class DirectedGraph
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<!-- ==================== CLASS DESCRIPTION ==================== -->
<h1 class="epydoc">Class DirectedGraph</h1><p class="nomargin-top"><span class="codelink"><a href="CedarBackup2.util-pysrc.html#DirectedGraph">source code</a></span></p>
<pre class="base-tree">
object --+
|
<strong class="uidshort">DirectedGraph</strong>
</pre>
<hr />
<p>Represents a directed graph.</p>
<p>A graph <b>G=(V,E)</b> consists of a set of vertices <b>V</b> together
with a set <b>E</b> of vertex pairs or edges. In a directed graph, each
edge also has an associated direction (from vertext <b>v1</b> to vertex
<b>v2</b>). A <code>DirectedGraph</code> object provides a way to
construct a directed graph and execute a depth- first search.</p>
<p>This data structure was designed based on the graphing chapter in <a
href="http://www2.toki.or.id/book/AlgDesignManual/" target="_top">The
Algorithm Design Manual</a>, by Steven S. Skiena.</p>
<p>This class is intended to be used by Cedar Backup for dependency
ordering. Because of this, it's not quite general-purpose. Unlike a
"general" graph, every vertex in this graph has at least one
edge pointing to it, from a special "start" vertex. This is so
no vertices get "lost" either because they have no dependencies
or because nothing depends on them.</p>
<!-- ==================== INSTANCE METHODS ==================== -->
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<td><span class="summary-sig"><a href="CedarBackup2.util.DirectedGraph-class.html#__init__" class="summary-sig-name">__init__</a>(<span class="summary-sig-arg">self</span>,
<span class="summary-sig-arg">name</span>)</span><br />
Directed graph constructor.</td>
<td align="right" valign="top">
<span class="codelink"><a href="CedarBackup2.util-pysrc.html#DirectedGraph.__init__">source code</a></span>
</td>
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<span class="summary-type"> </span>
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<td><span class="summary-sig"><a href="CedarBackup2.util.DirectedGraph-class.html#__repr__" class="summary-sig-name">__repr__</a>(<span class="summary-sig-arg">self</span>)</span><br />
Official string representation for class instance.</td>
<td align="right" valign="top">
<span class="codelink"><a href="CedarBackup2.util-pysrc.html#DirectedGraph.__repr__">source code</a></span>
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<span class="summary-type"> </span>
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<td><span class="summary-sig"><a href="CedarBackup2.util.DirectedGraph-class.html#__str__" class="summary-sig-name">__str__</a>(<span class="summary-sig-arg">self</span>)</span><br />
Informal string representation for class instance.</td>
<td align="right" valign="top">
<span class="codelink"><a href="CedarBackup2.util-pysrc.html#DirectedGraph.__str__">source code</a></span>
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<span class="summary-type"> </span>
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<td><span class="summary-sig"><a href="CedarBackup2.util.DirectedGraph-class.html#__cmp__" class="summary-sig-name">__cmp__</a>(<span class="summary-sig-arg">self</span>,
<span class="summary-sig-arg">other</span>)</span><br />
Definition of equals operator for this class.</td>
<td align="right" valign="top">
<span class="codelink"><a href="CedarBackup2.util-pysrc.html#DirectedGraph.__cmp__">source code</a></span>
</td>
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<span class="summary-type"> </span>
</td><td class="summary">
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<tr>
<td><span class="summary-sig"><a name="_getName"></a><span class="summary-sig-name">_getName</span>(<span class="summary-sig-arg">self</span>)</span><br />
Property target used to get the graph name.</td>
<td align="right" valign="top">
<span class="codelink"><a href="CedarBackup2.util-pysrc.html#DirectedGraph._getName">source code</a></span>
</td>
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<span class="summary-type"> </span>
</td><td class="summary">
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<tr>
<td><span class="summary-sig"><a href="CedarBackup2.util.DirectedGraph-class.html#createVertex" class="summary-sig-name">createVertex</a>(<span class="summary-sig-arg">self</span>,
<span class="summary-sig-arg">name</span>)</span><br />
Creates a named vertex.</td>
<td align="right" valign="top">
<span class="codelink"><a href="CedarBackup2.util-pysrc.html#DirectedGraph.createVertex">source code</a></span>
</td>
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</td>
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<span class="summary-type"> </span>
</td><td class="summary">
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<tr>
<td><span class="summary-sig"><a href="CedarBackup2.util.DirectedGraph-class.html#createEdge" class="summary-sig-name">createEdge</a>(<span class="summary-sig-arg">self</span>,
<span class="summary-sig-arg">start</span>,
<span class="summary-sig-arg">finish</span>)</span><br />
Adds an edge with an associated direction, from <code>start</code>
vertex to <code>finish</code> vertex.</td>
<td align="right" valign="top">
<span class="codelink"><a href="CedarBackup2.util-pysrc.html#DirectedGraph.createEdge">source code</a></span>
</td>
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<td width="15%" align="right" valign="top" class="summary">
<span class="summary-type"> </span>
</td><td class="summary">
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<tr>
<td><span class="summary-sig"><a href="CedarBackup2.util.DirectedGraph-class.html#topologicalSort" class="summary-sig-name">topologicalSort</a>(<span class="summary-sig-arg">self</span>)</span><br />
Implements a topological sort of the graph.</td>
<td align="right" valign="top">
<span class="codelink"><a href="CedarBackup2.util-pysrc.html#DirectedGraph.topologicalSort">source code</a></span>
</td>
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<span class="summary-type"> </span>
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<tr>
<td><span class="summary-sig"><a href="CedarBackup2.util.DirectedGraph-class.html#_topologicalSort" class="summary-sig-name" onclick="show_private();">_topologicalSort</a>(<span class="summary-sig-arg">self</span>,
<span class="summary-sig-arg">vertex</span>,
<span class="summary-sig-arg">ordering</span>)</span><br />
Recursive depth first search function implementing topological sort.</td>
<td align="right" valign="top">
<span class="codelink"><a href="CedarBackup2.util-pysrc.html#DirectedGraph._topologicalSort">source code</a></span>
</td>
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</td>
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<td colspan="2" class="summary">
<p class="indent-wrapped-lines"><b>Inherited from <code>object</code></b>:
<code>__delattr__</code>,
<code>__format__</code>,
<code>__getattribute__</code>,
<code>__hash__</code>,
<code>__new__</code>,
<code>__reduce__</code>,
<code>__reduce_ex__</code>,
<code>__setattr__</code>,
<code>__sizeof__</code>,
<code>__subclasshook__</code>
</p>
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<!-- ==================== CLASS VARIABLES ==================== -->
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<span class="summary-type"> </span>
</td><td class="summary">
<a name="_UNDISCOVERED"></a><span class="summary-name">_UNDISCOVERED</span> = <code title="0">0</code>
</td>
</tr>
<tr class="private">
<td width="15%" align="right" valign="top" class="summary">
<span class="summary-type"> </span>
</td><td class="summary">
<a name="_DISCOVERED"></a><span class="summary-name">_DISCOVERED</span> = <code title="1">1</code>
</td>
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<span class="summary-type"> </span>
</td><td class="summary">
<a name="_EXPLORED"></a><span class="summary-name">_EXPLORED</span> = <code title="2">2</code>
</td>
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<!-- ==================== PROPERTIES ==================== -->
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<span class="summary-type"> </span>
</td><td class="summary">
<a href="CedarBackup2.util.DirectedGraph-class.html#name" class="summary-name">name</a><br />
Name of the graph.
</td>
</tr>
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<td colspan="2" class="summary">
<p class="indent-wrapped-lines"><b>Inherited from <code>object</code></b>:
<code>__class__</code>
</p>
</td>
</tr>
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<!-- ==================== METHOD DETAILS ==================== -->
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<a name="__init__"></a>
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<h3 class="epydoc"><span class="sig"><span class="sig-name">__init__</span>(<span class="sig-arg">self</span>,
<span class="sig-arg">name</span>)</span>
<br /><em class="fname">(Constructor)</em>
</h3>
</td><td align="right" valign="top"
><span class="codelink"><a href="CedarBackup2.util-pysrc.html#DirectedGraph.__init__">source code</a></span>
</td>
</tr></table>
<p>Directed graph constructor.</p>
<dl class="fields">
<dt>Parameters:</dt>
<dd><ul class="nomargin-top">
<li><strong class="pname"><code>name</code></strong> (String value.) - Name of this graph.</li>
</ul></dd>
<dt>Overrides:
object.__init__
</dt>
</dl>
</td></tr></table>
</div>
<a name="__repr__"></a>
<div>
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cellspacing="0" width="100%" bgcolor="white">
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<table width="100%" cellpadding="0" cellspacing="0" border="0">
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<h3 class="epydoc"><span class="sig"><span class="sig-name">__repr__</span>(<span class="sig-arg">self</span>)</span>
<br /><em class="fname">(Representation operator)</em>
</h3>
</td><td align="right" valign="top"
><span class="codelink"><a href="CedarBackup2.util-pysrc.html#DirectedGraph.__repr__">source code</a></span>
</td>
</tr></table>
<p>Official string representation for class instance.</p>
<dl class="fields">
<dt>Overrides:
object.__repr__
</dt>
</dl>
</td></tr></table>
</div>
<a name="__str__"></a>
<div>
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cellspacing="0" width="100%" bgcolor="white">
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<h3 class="epydoc"><span class="sig"><span class="sig-name">__str__</span>(<span class="sig-arg">self</span>)</span>
<br /><em class="fname">(Informal representation operator)</em>
</h3>
</td><td align="right" valign="top"
><span class="codelink"><a href="CedarBackup2.util-pysrc.html#DirectedGraph.__str__">source code</a></span>
</td>
</tr></table>
<p>Informal string representation for class instance.</p>
<dl class="fields">
<dt>Overrides:
object.__str__
</dt>
</dl>
</td></tr></table>
</div>
<a name="__cmp__"></a>
<div>
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cellspacing="0" width="100%" bgcolor="white">
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<h3 class="epydoc"><span class="sig"><span class="sig-name">__cmp__</span>(<span class="sig-arg">self</span>,
<span class="sig-arg">other</span>)</span>
<br /><em class="fname">(Comparison operator)</em>
</h3>
</td><td align="right" valign="top"
><span class="codelink"><a href="CedarBackup2.util-pysrc.html#DirectedGraph.__cmp__">source code</a></span>
</td>
</tr></table>
<p>Definition of equals operator for this class.</p>
<dl class="fields">
<dt>Parameters:</dt>
<dd><ul class="nomargin-top">
<li><strong class="pname"><code>other</code></strong> - Other object to compare to.</li>
</ul></dd>
<dt>Returns:</dt>
<dd>-1/0/1 depending on whether self is <code><</code>,
<code>=</code> or <code>></code> other.</dd>
</dl>
</td></tr></table>
</div>
<a name="createVertex"></a>
<div>
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cellspacing="0" width="100%" bgcolor="white">
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<table width="100%" cellpadding="0" cellspacing="0" border="0">
<tr valign="top"><td>
<h3 class="epydoc"><span class="sig"><span class="sig-name">createVertex</span>(<span class="sig-arg">self</span>,
<span class="sig-arg">name</span>)</span>
</h3>
</td><td align="right" valign="top"
><span class="codelink"><a href="CedarBackup2.util-pysrc.html#DirectedGraph.createVertex">source code</a></span>
</td>
</tr></table>
<p>Creates a named vertex.</p>
<dl class="fields">
<dt>Parameters:</dt>
<dd><ul class="nomargin-top">
<li><strong class="pname"><code>name</code></strong> - vertex name</li>
</ul></dd>
<dt>Raises:</dt>
<dd><ul class="nomargin-top">
<li><code><strong class='fraise'>ValueError</strong></code> - If the vertex name is <code>None</code> or empty.</li>
</ul></dd>
</dl>
</td></tr></table>
</div>
<a name="createEdge"></a>
<div>
<table class="details" border="1" cellpadding="3"
cellspacing="0" width="100%" bgcolor="white">
<tr><td>
<table width="100%" cellpadding="0" cellspacing="0" border="0">
<tr valign="top"><td>
<h3 class="epydoc"><span class="sig"><span class="sig-name">createEdge</span>(<span class="sig-arg">self</span>,
<span class="sig-arg">start</span>,
<span class="sig-arg">finish</span>)</span>
</h3>
</td><td align="right" valign="top"
><span class="codelink"><a href="CedarBackup2.util-pysrc.html#DirectedGraph.createEdge">source code</a></span>
</td>
</tr></table>
<p>Adds an edge with an associated direction, from <code>start</code>
vertex to <code>finish</code> vertex.</p>
<dl class="fields">
<dt>Parameters:</dt>
<dd><ul class="nomargin-top">
<li><strong class="pname"><code>start</code></strong> - Name of start vertex.</li>
<li><strong class="pname"><code>finish</code></strong> - Name of finish vertex.</li>
</ul></dd>
<dt>Raises:</dt>
<dd><ul class="nomargin-top">
<li><code><strong class='fraise'>ValueError</strong></code> - If one of the named vertices is unknown.</li>
</ul></dd>
</dl>
</td></tr></table>
</div>
<a name="topologicalSort"></a>
<div>
<table class="details" border="1" cellpadding="3"
cellspacing="0" width="100%" bgcolor="white">
<tr><td>
<table width="100%" cellpadding="0" cellspacing="0" border="0">
<tr valign="top"><td>
<h3 class="epydoc"><span class="sig"><span class="sig-name">topologicalSort</span>(<span class="sig-arg">self</span>)</span>
</h3>
</td><td align="right" valign="top"
><span class="codelink"><a href="CedarBackup2.util-pysrc.html#DirectedGraph.topologicalSort">source code</a></span>
</td>
</tr></table>
<p>Implements a topological sort of the graph.</p>
<p>This method also enforces that the graph is a directed acyclic graph,
which is a requirement of a topological sort.</p>
<p>A directed acyclic graph (or "DAG") is a directed graph with
no directed cycles. A topological sort of a DAG is an ordering on the
vertices such that all edges go from left to right. Only an acyclic
graph can have a topological sort, but any DAG has at least one
topological sort.</p>
<p>Since a topological sort only makes sense for an acyclic graph, this
method throws an exception if a cycle is found.</p>
<p>A depth-first search only makes sense if the graph is acyclic. If the
graph contains any cycles, it is not possible to determine a consistent
ordering for the vertices.</p>
<dl class="fields">
<dt>Returns:</dt>
<dd>Ordering on the vertices so that all edges go from left to right.</dd>
<dt>Raises:</dt>
<dd><ul class="nomargin-top">
<li><code><strong class='fraise'>ValueError</strong></code> - If a cycle is found in the graph.</li>
</ul></dd>
</dl>
<div class="fields"> <p><strong>Note:</strong>
If a particular vertex has no edges, then its position in the final
list depends on the order in which the vertices were created in the
graph. If you're using this method to determine a dependency
order, this makes sense: a vertex with no dependencies can go
anywhere (and will).
</p>
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<h3 class="epydoc"><span class="sig"><span class="sig-name">_topologicalSort</span>(<span class="sig-arg">self</span>,
<span class="sig-arg">vertex</span>,
<span class="sig-arg">ordering</span>)</span>
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<p>Recursive depth first search function implementing topological
sort.</p>
<dl class="fields">
<dt>Parameters:</dt>
<dd><ul class="nomargin-top">
<li><strong class="pname"><code>vertex</code></strong> - Vertex to search</li>
<li><strong class="pname"><code>ordering</code></strong> - List of vertices in proper order</li>
</ul></dd>
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<h3 class="epydoc">name</h3>
<p>Name of the graph.</p>
<dl class="fields">
<dt>Get Method:</dt>
<dd class="value"><span class="summary-sig"><a href="CedarBackup2.util.DirectedGraph-class.html#_getName" class="summary-sig-name" onclick="show_private();">_getName</a>(<span class="summary-sig-arg">self</span>)</span>
- Property target used to get the graph name.
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