interlacing strings in python

Question

I had a question for a test where I had to interlace letters from two strings into one, I did it using the following code:

'abcd' and 'efghi' -> 'aebfcgdhi'

s1,s2='abcd' ,'efghi'
t=[a+b for a,b in zip(s1, s2) ]
ls1 = len(s1)
ls2 = len(s2)
if ls1 > ls2:
    t.extend(s1[ls2:])
elif ls1 < ls2:
    t.extend(s2[ls1:])
print ''.join(t)

I first tried using the following which seems to work only when strings are the same length or s2 is the longer string.

 print  ''.join([a+b for a,b in zip(s1, s2)]) + max(s1,s2)[min(len(s1),len(s2)):]

Where did I go wrong in my logic?

Possible duplicate of [interleaving 2 lists of unequal lengths](http://stackoverflow.com/questions/19883826/interleaving-2-lists-of-unequal-lengths) — Ashwini Chaudhary, Nov 13 '13 at 07:42
@hcwhsa I dont want to use itertools, my question is how to modify my own code to get required output or if it is possible at all so I can understand exactly how it works. — Padraic Cunningham, Nov 13 '13 at 07:47
@PadraicCunningham Have you checked DSM's [solution](http://stackoverflow.com/a/19884254/846892) on that thread? — Ashwini Chaudhary, Nov 13 '13 at 07:50
@PadraicCunningham Please check Edit 2 in my solution. That will make your sure that your program will work properly. — thefourtheye, Nov 13 '13 at 07:56
@hcwhsa I checked out all the answers, his solution works but I don't understand how it works as to me it is not very transparent , I don't need the answer to solve a question as I already have a working solution, I am trying to understand where my first solution went wrong. — Padraic Cunningham, Nov 13 '13 at 08:05
@PadraicCunningham You mean, you didnt understand my answer? — thefourtheye, Nov 13 '13 at 08:10
@thefourtheye, no I was talking about the answer that hcwhsa directed me to on another similar thread. — Padraic Cunningham, Nov 13 '13 at 08:12
I gave two duplicate links because of an ambiguity in the specification. — Karl Knechtel, Sep 06 '22 at 01:35

thefourtheye · Accepted Answer · 2013-11-13T08:11:54.423

1

To make your code work, you just need to use the key param in the max function

print  ''.join([a+b for a,b in zip(s1, s2)]) + max(s1,s2, key=len)[min(len(s1),len(s2)):]

Alternatively, you can use itertools.izip_longest to iterate till the biggest of the two iterables is exhausted. So, this solution works irrespective of the lengths of strings.

import itertools
s1,s2='abcd' ,'efghi'
print "".join(y for x in itertools.izip_longest(s1, s2) for y in x if y)

Output

aebfcgdhi

Edit:

Without using itertools

s1,s2='abcd' ,'efghi'
minLen = min(len(s1), len(s2))
print "".join(y for x in zip(s1, s2) for y in x) + s1[minLen:] + s2[minLen:]

edited Nov 13 '13 at 08:11

answered Nov 13 '13 at 07:40

thefourtheye

233,700
52
457
497

how to do it without using itertools? – Padraic Cunningham Nov 13 '13 at 07:43
@PadraicCunningham Please check now – thefourtheye Nov 13 '13 at 07:47
I have not seen the use of key before when using max. That was so simple, thanks very much – Padraic Cunningham Nov 13 '13 at 08:00

score 1 · Answer 2 · answered Nov 13 '13 at 07:46

1

Without using itertools.izip_longest:

>>> s1, s2 = 'abcd', 'efghi'
>>> l = min(len(s1), len(s2))
>>> ''.join(a+b for a, b in zip(s1, s2)) + s1[l:] + s2[l:]
'aebfcgdhi'

answered Nov 13 '13 at 07:46

falsetru

357,413
63
732
636

i know this is a very old thread, but since your solution worked perfectly, could you explain how to un-interlace it? – shamilpython Oct 30 '18 at 16:10
@shamilpython, Please post a separate question (not comment) with example. – falsetru Oct 30 '18 at 16:53

interlacing strings in python

2 Answers2