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POSimulating C-style for loops in python
 

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  1. POSimulating C-style for loops in python
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    <p>(even the title of this is going to cause flames, I realize)</p> <p>Python made the deliberate design choice to have the <code>for</code> loop use explicit iterables, with the benefit of considerably simplified code in most cases. </p> <p>However, sometimes it is quite a pain to construct an iterable if your test case and update function are complicated, and so I find myself writing the following while loops:</p> <pre><code>val = START_VAL while &lt;awkward/complicated test case&gt;: # do stuff ... val = &lt;awkward/complicated update&gt; </code></pre> <p>The problem with this is that the update is at the bottom of the <code>while</code> block, meaning that if I want to have a <code>continue</code> embedded somewhere in it I have to:</p> <ul> <li><p>use duplicate code for the complicated/awkard update, AND </p></li> <li><p>run the risk of forgetting it and having my code infinite loop</p></li> </ul> <p>I could go the route of hand-rolling a complicated iterator:</p> <pre><code>def complicated_iterator(val): while &lt;awkward/complicated test case&gt;: yeild val val = &lt;awkward/complicated update&gt; for val in complicated_iterator(start_val): if &lt;random check&gt;: continue # no issues here # do stuff </code></pre> <p>This strikes me as waaaaay too verbose and complicated. Do folks in stack overflow have a simpler suggestion?</p> <p>Response to comments:</p> <p>@Glenn Maynard: Yes, I dismissed the answer. It's bad to write five lines if there is a way to do it in one... especially in a case that comes up all the time (looping being a common feature of Turing-complete programs). </p> <p>For the folks looking for a concrete example: let's say I'm working with a custom date library. My question would then be, how would you express this in python: </p> <pre><code>for (date = start; date &lt; end; date = calendar.next_quarter_end(date)): if another_calendar.is_holiday(date): continue # ... do stuff... </code></pre>
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    1. COstore old val and immediately update val on the next line? and use oldval everywhere you used val before?
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    2. COA real code example would be nice. I've _never_ had to write code that awkward looking in Python...
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    3. COWhat's wrong with the first one? You need all those elements. Is it just that C allows all these on one line and python doesn't?
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