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    <blockquote> <p>If I were to do this in a very long running process, where lots of data was being consumed, would this "list" just continue consuming my memory until let go?</p> </blockquote> <p>Absolutely.</p> <blockquote> <p>When will the garbage collector claim the memory back? After the scope this list is built in is lost?</p> </blockquote> <p>CPython uses reference counting, so that is the most likely case. Other implementations work differently, so don't count on it.</p> <p>Thanks to Karl for pointing out that due to the complex memory management mechanisms used by CPython this does <em>not</em> mean that the memory is immediately returned to the OS after that.</p> <blockquote> <p>I don't know how the python garbage collector works, but I would venture to say that this list will exist until after the last next is called on all_stuff.</p> </blockquote> <p>I don't think <em>any</em> garbage collector works like that. Usually they mark-and-sweep, so it could be quite some time before the list is garbage collected.</p> <blockquote> <p>This is a common pattern found on list-comp how-to's.</p> </blockquote> <p>Absolutely not. The point is that you iterate the list with the purpose of doing something with every item (<code>do</code> is called for it's <a href="http://en.wikipedia.org/wiki/Side_effect_(computer_science)" rel="nofollow noreferrer"><em>side-effects</em></a>). In all the examples of the List-comp HOWTO, the list is iterated to <em>build up a new list</em> based on the items of the old one. Let's look at an example:</p> <pre><code># list comp, creates the list [0,1,2,3,4,5,6,7,8,9] [i for i in range(10)] # loop, does nothing for i in range(10): i # meh, just an expression which doesn't have an effect </code></pre> <p>Maybe you'll agree that this loop is utterly senseless, as it doesn't do anything, in contrary to the comprehension, which builds a list. In your example, it's the other way round: The comprehension is completely senseless, because you don't need the list! You can find more information about the issue on a <a href="https://stackoverflow.com/questions/5753597/is-it-pythonic-to-use-list-comprehensions-for-just-side-effects/5753614#5753614">related question</a></p> <p>By the way, if you really want to write that loop in one line, use a generator consumer like <code>deque.extend</code>. This will be slightly slower than a raw <code>for</code> loop in this simple example, though:</p> <pre><code>&gt;&gt;&gt; from collections import deque &gt;&gt;&gt; consume = deque(maxlen=0).extend &gt;&gt;&gt; consume(do(stuff) for stuff in all_stuff) </code></pre>
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    1. COCan you do some `timeit` benchmarks for your last code block?
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    2. CO@Blender: Meh, can't seem to be able to prove this... Thanks for forcing me to learn it the hard way :P
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    3. COThere was a question some time ago about that: [Passing iterators to any for execution for speed and Why?](http://stackoverflow.com/q/9144934/1132524)
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