python most efficient substring method

Question

lets say we have a very big string. and we want to display only 100 characters in the stdout. and the remaining will go to the next line. my first method will be using index slicing and set the startIndex to increment by 100 and so on:

while (veryLargeStringLength/100 > 0):
    startIndex = 0
    veryLargeString[startIndex :startIndex+100]
    startIndex += 100
    veryLargeStringLength -= 100

Is this the most efficient way to do this? Any other optimization method? I would say that there is no point in cosidering multiThreaded or multiprocessing in this scenario?

Thanks

I'd advise you to time your code before trying to optimize it. In this case the operation is much faster than printing no almost no matter how you do it, and writing it clearly (as in Ashwini's answer below) is more important (also: just as fast). — U2EF1
– U2EF1, Commented Jun 4, 2013 at 4:34
@U2EF1 +1. Only worry about optimizing code if you are sure that it is not working fast enough. There is almost always a more efficient way to do things, but why rack your brain over it, if the current approach is suitable for your immediate needs? — David Zemens
– David Zemens, Commented Jun 4, 2013 at 4:51

Ashwini Chaudhary · Accepted Answer · 2013-06-04 05:18:22Z

4

Something like this:

n = 100
for i in xrange(0, len(strs), n):
    print strs[i:i+n]

working version of your code:

veryLargeStringLength = len(strs)
startIndex = 0                     #this should be before the loop
while veryLargeStringLength > 0:   #use just >0, no need of division
    print veryLargeString[startIndex :startIndex+100]
    startIndex += 100
    veryLargeStringLength -= 100

edited Jun 4, 2013 at 5:18

answered Jun 4, 2013 at 4:22

Ashwini Chaudhary

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3 Comments

aldeb Over a year ago

I think while very_large_string_length > 0: would be much more readable and in accordance with the PEP8's recommendations: python.org/dev/peps/pep-0008/#other-recommendations

oleg Over a year ago

isn't better to use veryLargeStringLength > startIndex: instead without decreasing of veryLargeStringLength

user2450170 Over a year ago

thank you for fixing my incomplete codes. Actually I have tried using the xrange. however it is slower than the normal implementation. will it be feasible to use multithread or multiprocessing in this type of scenario?

Abhinav · Accepted Answer · 2013-06-05 22:11:31Z

0

You can use python built-in method range(start, stop[, step]) to achieve this. Start with 0, Stop at the end of the string (i.e. length of the string) and traverse in the steps of 100

for group_of_char in [veryLargeString[i:i+100] for i in range(0, len(veryLargeString), 100)]:
    print group_of_char

Or better convert this logic into a method and call as suited

def slice_string_in_n_size_pieces(input_string, n_size):
    return [input_string[i:i+n_size] for i in range(0, len(input_string), n_size)]

answered Jun 5, 2013 at 22:11

Abhinav

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