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copied!<p>There's no prepackaged "do-while", but the general Python way to implement peculiar looping constructs is through generators and other iterators, e.g.:</p> <pre><code>import itertools def dowhile(predicate): it = itertools.repeat(None) for _ in it: yield if not predicate(): break </code></pre> <p>so, for example:</p> <pre><code>i=7; j=3 for _ in dowhile(lambda: i<j): print i, j i+=1; j-=1 </code></pre> <p>executes one leg, as desired, even though the predicate's already false at the start.</p> <p>It's normally better to encapsulate more of the looping logic into your generator (or other iterator) -- for example, if you often have cases where one variable increases, one decreases, and you need a do/while loop comparing them, you could code:</p> <pre><code>def incandec(i, j, delta=1): while True: yield i, j if j <= i: break i+=delta; j-=delta </code></pre> <p>which you can use like:</p> <pre><code>for i, j in incandec(i=7, j=3): print i, j </code></pre> <p>It's up to you how much loop-related logic you want to put inside your generator (or other iterator) and how much you want to have outside of it (just like for any other use of a function, class, or other mechanism you can use to refactor code out of your main stream of execution), but, generally speaking, I like to see the generator used in a <code>for</code> loop that has little (ideally none) "loop control logic" (code related to updating state variables for the next loop leg and/or making tests about whether you should be looping again or not).</p>

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