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POpython lazy variables? or, delayed expensive computation
 

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  1. POpython lazy variables? or, delayed expensive computation
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    <p>I have a set of arrays that are very large and expensive to compute, and not all will necessarily be needed by my code on any given run. I would like to make their declaration optional, but ideally without having to rewrite my whole code.</p> <p>Example of how it is now:</p> <pre><code>x = function_that_generates_huge_array_slowly(0) y = function_that_generates_huge_array_slowly(1) </code></pre> <p>Example of what I'd like to do:</p> <pre><code>x = lambda: function_that_generates_huge_array_slowly(0) y = lambda: function_that_generates_huge_array_slowly(1) z = x * 5 # this doesn't work because lambda is a function # is there something that would make this line behave like # z = x() * 5? g = x * 6 </code></pre> <p>While using lambda as above achieves one of the desired effects - computation of the array is delayed until it is needed - if you use the variable "x" more than once, it has to be computed each time. I'd like to compute it only once.</p> <p>EDIT: After some additional searching, it looks like it is possible to do what I want (approximately) with "lazy" attributes in a class (e.g. <a href="http://code.activestate.com/recipes/131495-lazy-attributes/" rel="noreferrer">http://code.activestate.com/recipes/131495-lazy-attributes/</a>). I don't suppose there's any way to do something similar without making a separate class?</p> <p>EDIT2: I'm trying to implement some of the solutions, but I'm running in to an issue because I don't understand the difference between:</p> <pre><code>class sample(object): def __init__(self): class one(object): def __get__(self, obj, type=None): print "computing ..." obj.one = 1 return 1 self.one = one() </code></pre> <p>and</p> <pre><code>class sample(object): class one(object): def __get__(self, obj, type=None): print "computing ... " obj.one = 1 return 1 one = one() </code></pre> <p>I think some variation on these is what I'm looking for, since the expensive variables are intended to be part of a class.</p>
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    1. COhttp://stackoverflow.com/questions/5078726/setting-a-property-inside-a-python-method is a more useful implementation of laziness for what I'm trying to do
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