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POHierarchy / Flyweight / Instancing Problem in Python
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copied!<p>Here is the problem I am trying to solve, (I have simplified the actual problem, but this should give you all the relevant information). I have a hierarchy like so:</p> <pre><code>1.A 1.B 1.C 2.A 3.D 4.B 5.F </code></pre> <p>(This is hard to illustrate - each number is the parent, each letter is the child).</p> <ol> <li><p>Creating an instance of the 'letter' objects is expensive (IO, database costs, etc), so should only be done once.</p></li> <li><p>The hierarchy needs to be easy to navigate.</p></li> <li><p>Children in the hierarchy need to have just one parent.</p></li> <li><p>Modifying the contents of the letter objects should be possible directly from the objects in the hierarchy.</p></li> <li><p>There needs to be a central store containing all of the 'letter' objects (and only those in the hierarchy).</p></li> <li><p>'letter' and 'number' objects need to be possible to create from a constructor (such as Letter(**kwargs) ).</p></li> <li><p>It is perfectably acceptable to expect that when a letter changes from the hierarchy, all other letters will respect the same change.</p></li> </ol> <p>Hope this isn't too abstract to illustrate the problem.</p> <p>What would be the best way of solving this? (Then I'll post my solution)</p> <p>Here's an example script:</p> <pre><code>one = Number('one') a = Letter('a') one.addChild(a) two = Number('two') a = Letter('a') two.addChild(a) for child in one: child.method1() for child in two: print '%s' % child.method2() </code></pre>

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