http://code.activestate.com/recipes/tags/lazy_evaluation-algorithm/2010-01-15T06:08:56-08:00ActiveState Code Recipes2009-04-26T18:10:55-07:00Sridhar Ratnakumarhttp://code.activestate.com/recipes/users/4169511/http://code.activestate.com/recipes/576720-lazy-property/

<p style="color: grey"> Python recipe 576720 by <a href="/recipes/users/4169511/">Sridhar Ratnakumar</a> (<a href="/recipes/tags/evaluation/">evaluation</a>, <a href="/recipes/tags/lazy/">lazy</a>, <a href="/recipes/tags/lazy_evaluation/">lazy_evaluation</a>). Revision 6. </p> <p>Python does not have lazy evaluation syntax features built-in, but fortunately decorators can be used with new-style classes to emulate such a feature. There are cases where one wants <code>foo.property</code> to return the actual property whose calculation takes significant amount of time.</p> <p>This recipe adapts the existing <code>property</code> to provide a <code>lazypropery</code> decorator that does this.</p> <p>See the first comment below for an example usage.</p> <p>Also see: <a href="http://en.wikipedia.org/wiki/Lazy_initialization">lazy initialization</a></p>

2010-01-15T06:08:56-08:00Eric-Olivier LE BIGOThttp://code.activestate.com/recipes/users/2672032/http://code.activestate.com/recipes/576721-calculations-with-error-propagation-and-semi-forma/

<p style="color: grey"> Python recipe 576721 by <a href="/recipes/users/2672032/">Eric-Olivier LE BIGOT</a> (<a href="/recipes/tags/calculus/">calculus</a>, <a href="/recipes/tags/error_propagation/">error_propagation</a>, <a href="/recipes/tags/expressions/">expressions</a>, <a href="/recipes/tags/formal_calculations/">formal_calculations</a>, <a href="/recipes/tags/lazy_evaluation/">lazy_evaluation</a>, <a href="/recipes/tags/uncertainties/">uncertainties</a>). Revision 22. </p> <p><strong>Do not use this module</strong>, but use instead the more powerful <a href="http://pypi.python.org/pypi/uncertainties/">uncertainties.py module</a>.</p> <p>Module for performing calculations with error propagation, such as (1 +- 0.1) * 2 = 2 +- 0.2. Mathematical operations (addition, etc.), operations defined in the math module (sin, atan,...) and logical operations (&lt;, &gt;, etc.) can be used.</p> <p>Correlations between parts of an expression are correctly taken into account (for instance, the error on "x-x" is strictly zero).</p> <p>Code written for floats should directly work with the numbers with uncertainty defined here, without much need for modifications.</p> <p>The module also contains a class that represents non-evaluated mathematical expressions. This class is used for performing the differentiation required by the error propagation calculation, but can be used on its own, for manipulating "semi-formal" expressions whose variables can be accessed.</p>