<div dir="ltr">Doug,<div><br></div><div>Also, I didn't see your question get answered.</div><div><br></div><div>"The" answer to why is recursion expensive vs iteration is stack traces. See Guido's answer <a href="https://t.yesware.com/tt/6640a48a14dbdef70b47105ac6b72156559fc5a6/5ba2375237a9fdc8efa681b19014981f/d6c3025efb0710ebe9f6fa425f843d2c/plus.google.com/115212051037621986145/posts/HajXHPGN752">here</a> or try it yourself as mentioned <a href="http://t.yesware.com/tt/6640a48a14dbdef70b47105ac6b72156559fc5a6/5ba2375237a9fdc8efa681b19014981f/dda1509570b2b5d9d162e6293a1b3f07/stackoverflow.com/questions/22893139/why-is-a-function-method-call-in-python-expensive">here</a>.</div><div><br></div><div>Recursion means creating more functions / stack traces.</div><img src="https://t.yesware.com/t/6640a48a14dbdef70b47105ac6b72156559fc5a6/5ba2375237a9fdc8efa681b19014981f/spacer.gif" style="border:0; width:0; height:0; overflow:hidden;" width="0" height="0"><img src="http://t.yesware.com/t/6640a48a14dbdef70b47105ac6b72156559fc5a6/5ba2375237a9fdc8efa681b19014981f/spacer.gif" style="border:0; width:0; height:0; overflow:hidden;" width="0" height="0"><font face="yw-6640a48a14dbdef70b47105ac6b72156559fc5a6-5ba2375237a9fdc8efa681b19014981f--tol" style="display: none;"></font></div><div class="gmail_extra"><br><div class="gmail_quote">On Thu, Feb 18, 2016 at 7:55 PM, Adam Forsyth <span dir="ltr"><<a href="mailto:adam@adamforsyth.net" target="_blank">adam@adamforsyth.net</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><p dir="ltr">Phil,</p>
<p dir="ltr">That's generally true, but one small correction. Aaron's solution won't actually won't flatten strings, as they don't have "__iter__" methods. They implement iteration because they take sequential numeric indexes starting at 0, and raise an IndexError after the index passed is too large. </p><span class="HOEnZb"><font color="#888888">
<p dir="ltr">Adam </p>
</font></span><div class="gmail_quote"><div><div class="h5">On Feb 18, 2016 19:22, "Robare, Phillip (TEKSystems)" <<a href="mailto:proba@allstate.com" target="_blank">proba@allstate.com</a>> wrote:<br type="attribution"></div></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div><div class="h5">
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1f497d">Aaron, unlike Massimo’s elegant one-liner you don’t check that what you are iterating over is a list. Since Python will happily iterate over strings, dictionaries,
and much more you quickly get into problems when the list includes more types than lists and numbers. I recount this from experience when I tried to throw together a flatten routine and pass it a data structure that I got from loading a JSON string.<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1f497d"><u></u> <u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif;color:#1f497d">Phil Robare<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1f497d"><u></u> <u></u></span></p>
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<p class="MsoNormal"><b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif"><snip/><u></u><u></u></span></b></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif"><u></u> <u></u></span></p>
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<p class="MsoNormal">On Thu, Feb 18, 2016 at 1:43 PM, Aaron Elmquist <<a href="mailto:elmq0022@umn.edu" target="_blank">elmq0022@umn.edu</a>> wrote:<u></u><u></u></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt">Douglas, <u></u><u></u></p>
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<p class="MsoNormal">Here's one more version for you and the rest of the list. It's based on Brad's code. I will let you think about why this version might be better or worse. Also, recursion is great. It's just too bad it's not one of python's strong points.<u></u><u></u></p>
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<br>
def flatten(lst):<br>
for item1 in lst:<br>
if hasattr(item1, '__iter__'):<br>
for item2 in flatten(item1):<br>
yield item2<br>
else:<br>
yield item1<br>
<br>
print([x for x in flatten([1, [2,3,[4,5,6,[7,8,9]]]]) if x%2 == 1])<br>
<br>
y = flatten([1, [2,3,[4,5,6,[7,8,9]]]])<br>
<br>
print(next(y))<br>
print(next(y))<br>
print(next(y))<br>
.<br>
.<br>
.<br>
<snip/><u></u><u></u></p>
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<p class="MsoNormal">On Wed, Feb 17, 2016 at 9:48 PM, DiPierro, Massimo <<a href="mailto:MDiPierro@cs.depaul.edu" target="_blank">MDiPierro@cs.depaul.edu</a>> wrote:<u></u><u></u></p>
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<p class="MsoNormal" style="margin-left:46.2pt">here is a one liner:<br>
<br>
def flatten(x):<br>
return [z for y in x for z in flatten(y)] if isinstance(x,list) else [x]<br>
<br>
<br>
<u></u><u></u></p>
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