Python basic string split method behaviour

Question

I have the following function which I used to find the length of the places in a binary number where zeros are encapsulated by ones:

def solution(N):
# write your code in Python 2.7
# convert to binary
binary = bin(N)[2:] # results prefixed with '0b'
# special case of no zeros
if '0' not in str(binary):
    print('No binary gap in %s'% str(binary))
    return 0
# special case of all zeros after first 1
if '1' not in str(binary)[1:]:
    print('No binary gap in %s'% str(binary))
    return 0
# special case of N == 1 = 01
if N == 1:
    print('No binary gap in %s'% str(binary))
    return 0

bgaps = []
sbin = str(binary)
print(sbin)
spbin = sbin.split('1')
print(spbin)
for i in spbin:
    if i == '': continue
    bgaps.append(len(i))

return max(bgaps)

for N in [6,328,147,15,2,483,647]:
    print(solution(N)

The results show that string split doesn't always return a '' where the delimiter used to be. The happens e.g. for 101001000 where the split returns

['', '0', '00', '000']

instead of

['', '0','', '00', '', '000']

I suspect that this has to do with a special meaning of '01' but the delimiter is '1'. Any thoughts on why this split behaves this way?

split throws away the delimiter: "a,b,c".split(',') == ["a", "b", "c"]. — ForceBru
– ForceBru, Commented Aug 10, 2017 at 21:06

Moses Koledoye · Accepted Answer · 2017-08-10 21:22:01Z

4

You seem to misunderstand how str.split works. Since 1 is at the start of the string, the empty string appears on the left side of the split at the start character; str.split puts this into consdiration:

>>> '1'.split('1')
['', '']

Looks like you don't want to split.

You probably want something of the sort:

>>> from itertools import groupby
>>> sbin = '101001000'
>>> ['' if k=='1' else ''.join(g)  for k, g in groupby(sbin)]
['', '0', '', '00', '', '000']

edited Aug 10, 2017 at 21:22

answered Aug 10, 2017 at 21:03

Moses Koledoye

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3 Comments

Chris Over a year ago

I was going to post a solution with groupby too, but it appears as if the OP is doing homework, in which case using something like gropuby would probably be considered cheating. Maybe provide a hand-rolled solution as well?

Moses Koledoye Over a year ago

@ChristianDean I added that since they've shown some effort at working the larger part 'alone' :)

Shejo284 Over a year ago

@ Moses Koledoye Appreciate the clarification. This question is not "homework" just learning python via the "Codility" and GeeksforGeeks websites.

Anton vBR · Accepted Answer · 2017-08-10 21:22:09Z

2

Update Added exception if last element is a 1.

How about replacing the "1" with "11" adding an empty space between.

sbin = '10100100'

if sbin[-1] == "1":
    print(sbin.replace("1","11").split("1")[1:-1]) # remove first and last
else:
    print(sbin.replace("1","11").split("1")[1:]) # remove first

prints

['', '0', '', '00', '', '000']

edited Aug 10, 2017 at 21:22

answered Aug 10, 2017 at 21:16

Anton vBR

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1 Comment

Shejo284 Over a year ago

An interesting solution :-)

itsmewiththeface · Accepted Answer · 2017-08-10 21:19:10Z

2

As @ForceBru mentioned, split removes the delimiter which is the same behavior in a lot of languages. You probably want to approach this differently (perhaps using a combination of split + replace or something similar to count the gaps).

Hope that provides some insight.

answered Aug 10, 2017 at 21:19

itsmewiththeface

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