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    <p>If you change:</p> <pre><code>return lo,pi,hi,len(lo)+1 </code></pre> <p>to:</p> <pre><code>return lo,pi,hi,len(lo) </code></pre> <p>and add a closing bracket <code>)</code> so that the syntax error is corrected, like so:</p> <pre><code>lo,pi,hi,loc_pi= random_partition(seq) </code></pre> <p>It will work reliably for sequences with no repeated entries:</p> <pre><code>for i in xrange(1,8): print rselect([54,-1,1000,565,64,2,5],7,i), #Output: -1 2 5 54 64 565 [1000] </code></pre> <p>Which is the expected output. </p> <p>I guess my main advice would be to try and code following the <a href="http://www.python.org/dev/peps/pep-0008/" rel="nofollow">style guidlines!</a> Your code is pretty tricky to read at a glance!</p> <p>The parameter <code>length</code> is redundant, so can be removed altogether. And also sometimes the last entry would be returned as a single value list, so I've changed that (although it will know fall over if you pass it an empty list, probably not a big deal). Here is the code in slightly more readable format, with a correction to allow for repeated entries:</p> <pre><code>from random import choice, shuffle def rselect(seq, i):     lo, hi, pi, loc_pi = random_partition(seq)     if loc_pi == i or (min(lo) == max(lo) and not hi):         return pi     elif loc_pi &gt; i:         return rselect(lo, i)     elif loc_pi &lt; i:         return rselect(hi, i - loc_pi) def random_partition(seq):     pi = choice(seq)     lo = [x for x in seq if x &lt;= pi]     hi = [x for x in seq if x &gt; pi]     return lo, hi, pi, len(lo) #this is a nice way to test it: cat = range(1,21) for i in xrange(1,21):     shuffle(cat)     print rselect(cat,i), #Output: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 </code></pre>
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    1. PORandomised select in python, working unexpectedly
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    1. USfraxel
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    1. COI dont really think it solves the problem. I dont see the statistic printed as a result. Could you elaborate what your solution does? I tried it using my input sequence , the solution works in some cases and doesnt in others for instance `test_rselect([54,-1,1000,56,5,64,2,5],3)` returns an IndexError on line `if loc_pi>i:return rselect(lo,loc_pi+1,i) `. Do improve your answer. Thanks!
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      1. USKodeSeeker
    2. CO@KodeSeeker - I've updated to allow for repeated elements in the input sequence (thats what the problem was with: `[54,-1,1000,56,5,64,2,5]`).
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      1. USfraxel
    3. COWhat does your input sequence really do ? I dont see what happens with `rselect(cat,i)` there .Could you please explain the test function?
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