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POGiven this same piece of code, why is the python version 100x+ slower than C?
 

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  1. POGiven this same piece of code, why is the python version 100x+ slower than C?
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    <p>I'm doing project euler Q14.</p> <blockquote> <p>Which starting number, under one million, produces the longest collatz chain?</p> </blockquote> <p>I was very surprised to see someone who could get a result in 0.7sec. More surprised when I see it is merely a naive brute force solution.</p> <p>I was skeptical as I spent so much time to optimize my python version, getting the runtime down to about a minute. So I ran the code myself... OP wasn't lying. </p> <p>I translated the same code to Python, it failed to terminate after 5 minutes.</p> <p>What gives?</p> <p>C version : <a href="http://codepad.org/VD9QJDkt" rel="nofollow">http://codepad.org/VD9QJDkt</a></p> <pre><code>#include &lt;stdio.h&gt; #include &lt;time.h&gt; int main(int argc, char **argv) { int longest = 0; int terms = 0; int i; unsigned long j; clock_t begin, end; double time_spent; begin = clock(); for (i = 1; i &lt;= 1000000; i++) { j = i; int this_terms = 1; while (j != 1) { this_terms++; if (this_terms &gt; terms) { terms = this_terms; longest = i; } if (j % 2 == 0) { j = j / 2; } else { j = 3 * j + 1; } } } printf("longest: %d (%d)\n", longest, terms); end = clock(); time_spent = (double)(end - begin) / CLOCKS_PER_SEC; printf("It took %f seconds\n", time_spent); return 0; } </code></pre> <p>Python version: <a href="http://codepad.org/ZloPyEcz" rel="nofollow">http://codepad.org/ZloPyEcz</a></p> <pre><code>import time def iterative_brute_force(n): longest = 0 terms = 0 for i in range(1, n + 1): j = i this_terms = 1 while j != 1: this_terms += 1 if this_terms &gt; terms: terms = this_terms longest = i if j % 2 == 0: j = j / 2 else: j = 3 * j + 1 return longest, terms t0 = time.time() print(iterative_brute_force(10 ** 6)) t1 = time.time() total = t1-t0 print(total) </code></pre>
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      1. POGiven this same piece of code, why is the python version 100x+ slower than C?
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      1. POGiven this same piece of code, why is the python version 100x+ slower than C?
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      1. POGiven this same piece of code, why is the python version 100x+ slower than C?
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    1. CODo you expect python to run faster than c? Also, i think the problem is in your python algorithm..
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      1. POGiven this same piece of code, why is the python version 100x+ slower than C?
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    2. COYou should see [this](http://code.jasonbhill.com/c/project-euler-problem-14/)
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      1. POGiven this same piece of code, why is the python version 100x+ slower than C?
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    3. CO@aIKid I don't think the surprise is that it's slower but that it takes *so much* (at least 300x) more time. And the algorithm is the same for both programs, so that's *not* the problem.
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