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PODetecting if an iterator will be consumed
 

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  1. PODetecting if an iterator will be consumed
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    <p>Is there an uniform way of knowing if an iterable object will be consumed by the iteration?</p> <p>Suppose you have a certain function <code>crunch</code> which asks for an iterable object for parameter, and uses it many times. Something like:</p> <pre><code>def crunch (vals): for v in vals: chomp(v) for v in vals: yum(v) </code></pre> <p>(note: merging together the two <code>for</code> loops is not an option).</p> <p>An issue arises if the function gets called with an iterable which is not a list. In the following call the <code>yum</code> function is never executed:</p> <pre><code>crunch(iter(range(4)) </code></pre> <p>We could in principle fix this by redefining the <code>crunch</code> function as follows:</p> <pre><code>def crunch (vals): vals = list(vals) for v in vals: chomp(v) for v in vals: yum(v) </code></pre> <p>But this would result in using twice the memory if the call to <code>crunch</code> is:</p> <pre><code>hugeList = list(longDataStream) crunch(hugeList) </code></pre> <p>We could fix this by defining <code>crunch</code> like this:</p> <pre><code>def crunch (vals): if type(vals) is not list: vals = list(vals) for v in vals: chomp(v) for v in vals: yum(v) </code></pre> <p>But still there colud be the case in which the calling code stores data in something which</p> <ul> <li>cannot be consumed</li> <li>is not a list</li> </ul> <p>For instance:</p> <pre><code>from collections import deque hugeDeque = deque(longDataStream) crunch(hugeDeque) </code></pre> <p>It would be nice to have a <code>isconsumable</code> predicate, so that we can define <code>crunch</code> like this:</p> <pre><code>def crunch (vals): if isconsumable(vals): vals = list(vals) for v in vals: chomp(v) for v in vals: yum(v) </code></pre> <p>Is there a solution for this problem?</p>
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    1. COAre you expecting only lists in this function?
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      1. USHenrik Andersson
    2. CO`if isinstance(vals, collections.Iterator)` is similar to what you want
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    3. CO@Volatility: `Iterator` is not the appropriate choice, since an iterator still might be consumed.
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      1. USBrenBarn
 

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