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POPython: Handling exceptions while sorting
 

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    <p>I have a list of objects that I need to sort according to a <a href="https://wiki.python.org/moin/HowTo/Sorting/#Key_Functions" rel="nofollow" title="Key functions">key function</a>. The problem is that some of the elements in my list can go "out-of-date" while the list is being sorted. When the key function is called on such an expired item, it fails with an exception.</p> <p>Ideally, what I would like is a way of sorting my list with a key function such that when an error occurs upon calling the key function on an element, this element is excluded from the sort result.</p> <p>My problem can be reconstructed using the following example: Suppose I have two classes, <code>Good</code> and <code>Bad</code>:</p> <pre><code>class Good(object): def __init__(self, x): self.x = x def __repr__(self): return 'Good(%r)' % self.x class Bad(object): @property def x(self): raise RuntimeError() def __repr__(self): return 'Bad' </code></pre> <p>I want to sort instances of these classes according to their <code>x</code> property. Eg.:</p> <pre><code>&gt;&gt;&gt; sorted([Good(5), Good(3), Good(7)], key=lambda obj: obj.x) [Good(3), Good(5), Good(7)] </code></pre> <p>Now, when there is a <code>Bad</code> in my list, the sorting fails:</p> <pre><code>&gt;&gt;&gt; sorted([Good(5), Good(3), Bad()], key=lambda obj: obj.x) ... RuntimeError </code></pre> <p>I am looking for a magical function <code>func</code> that sorts a list according to a key function, but simply ignores elements for which the key function raised an error:</p> <pre><code>&gt;&gt;&gt; func([Good(5), Good(3), Bad()], key=lambda obj: obj.x) [Good(3), Good(5)] </code></pre> <p>What is the most Pythonic way of achieving this?</p>
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    1. CODoes `Bad.x` really raise a `RuntimeError` when asked for or does it simply raise an `AttributeError`?
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    2. COI'm curious as to why your objects expire. Is it another thread, modifying your objects while you sort? Or do they literally expire due to the passage of time? But then, why would that make the attribute raise an Exception? For instance, it's not sensible to make the attribute `Apple.age` raise a `TooOldException`.
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    3. CO@Kevin, the objects expire because they represent (Selenium) web elements in an open browser window (=another process). If eg. the page reloads while the list is being sorted, then at least some elements of the list raise Selenium `StaleElementReferenceExceptions` when accessing their attributes.
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