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POCreating lists from huge object taking more time than creating it from huge file
 

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  1. POCreating lists from huge object taking more time than creating it from huge file
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    <p>I was working with a huge file today when I found this. My mind = blown, till now I always used to create a single in memory object from file and used to do all my stuff on that object. </p> <p>Consider this use case where I am creating a huge file (for clarity sake) and then reading it into 2 different lists. </p> <pre><code>import csv import time TEMP_FILE_NAME = '/tmp/foo.csv' def write_huge_file(): with open(TEMP_FILE_NAME, 'wb') as f: writer = csv.writer(f) writer.writerows((((i, i + 100) for i in xrange(29999999)))) def get_file_iterator(): with open(TEMP_FILE_NAME, 'rb') as f: reader = csv.reader(f, delimiter=',') for row in reader: yield row def make_2_list_from_object(): file_iterator = get_file_iterator() main_list = [(i, j) for i, j in file_iterator] list1 = [i[0] for i in main_list] list2 = [i[1] for i in main_list] def make_2_list_from_file(): list1 = list(i[0] for i in get_file_iterator()) list2 = list(i[1] for i in get_file_iterator()) if __name__ == '__main__': #write_huge_file() # Uncomment this to write the file once print 'wrote_file' a = time.time() make_2_list_from_file() b = time.time() print b-a make_2_list_from_object() c = time.time() print 'Time taken using file: ', str(b-a) print 'Time taken using object: ', str(c-b) </code></pre> <p>Now when I run it I get this output:</p> <pre><code>Time taken using file: 49.212211132 s Time taken using object: 1018.5052530766 s </code></pre> <p>Can anyone please explain this to me? I am thinking its because of python's swap memory usage when it runs out of RAM.</p> <p>Also please note that I had 4 Gigs of RAM while running this program. You can increase the number of lines in written file if you have more RAM to reproduce this.</p>
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    1. PTQuestion
    1. USHooked
    1. USRafi
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    2. VO
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      1. VTUpMod
    1. COIt's a bad idea to post your email address in the question of the post (nor does it add any value to the question). I've removed it for you in this question.
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      1. USHooked
    2. COOops sorry, It came in as a snippet in vim :/
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      1. USRafi
    3. COFor smaller files, I get the reverse timing, i.e. using an intermediate list is fast. This would suggest that you exhaust your memory :)
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      1. USDavid Zwicker
 

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