How to intersperse characters from two different strings alternatively to form a string

Question

Method1:

    abc = 'Hello World'
    qwe = 'abc 123'
    
    #intersperse words
    def intersperse(abc,qwe):
        list = []
        for i in abc:
            list.append(i)
            for j in qwe:
                list.append(j)
        return ''.join(list)
    
    intersperse(abc,qwe)

Output: "Habc 123eabc 123labc 123labc 123oabc 123 abc 123Wabc 123oabc 123rabc 123labc 123dabc 123"

Method 2:

    #intersperse words
    def intersperse(abc,qwe):
        abcs = abc.split()
        qwes = qwe.split()
        result = sum(zip(abcs, qwes+[0]), ())[:-1]
        return ''.join(result)
    
    intersperse(abc,qwe)

Output: "HelloabcWorld" (<--somehow the 123 is missing)

Tried both methods but couldn't get it to work. I want the output to also take into consideration the blanks in between the characters as well.

Desired output: "Haeblcl o1 2W3orld"

score 4 · Accepted Answer · answered May 23 '22 at 12:19

What about a simple for-loop inside a list comprehension to shorten the matter?

def intersperse(abc,qwe):
    min_len = min(len(abc), len(qwe))
    return "".join([abc[i] + qwe[i] for i in range(min_len)]) + abc[min_len:] + qwe[min_len:]

Explanation: determine the min length of both strings - up to that length, alternatingly add characters of both strings. Finally, add the leftover characters of the longer string, leveraging slicing.

The output is as expected: intersperse("Hello World", "abc 123") yields 'Haeblcl o1 2W3orld'.

Arwalk · Answer 2 · 2022-05-23T12:51:12.657

It's easily done with a generator function.

abc = 'Hello World'
qwe = 'abc 123'

def intersperce(a, b):
    if len(a) > len(b):
        filler = a[len(b):]
    else:
        filler = b[len(a):]

    def generator():
        for char_a, char_b in zip(a, b):
            yield char_a
            yield char_b
        for x in filler:
            yield x

    return "".join(generator())


assert intersperce(abc, qwe) == "Haeblcl o1 2W3orld"

yield returns the value and suspend execution. Just by iterating over a zip on (a, b), you can easily yield one character at a time. Then just have to fill with the remaining characters.

You can refer to the official documentation about it!

EDIT:

I didn't know about zip_longest, thanks @Nin17. Here is a shorter version that doesn't need a filler.

from itertools import zip_longest

abc = 'Hello World'
qwe = 'abc 123'

def intersperce(a, b):

    def generator():
        for char_a, char_b in zip_longest(a, b, fillvalue=""):
            yield char_a
            yield char_b

    return "".join(generator())


assert intersperce(abc, qwe) == "Haeblcl o1 2W3orld"

which leads me to the code golf version

from itertools import zip_longest

abc = 'Hello World'
qwe = 'abc 123'


def intersperce(a, b):
    return "".join(i + j for i, j in zip_longest(a, b, fillvalue=""))


assert intersperce(abc, qwe) == "Haeblcl o1 2W3orld"

Nin17 · Answer 3 · 2022-05-23T12:54:35.870

1

You can use itertools zip_longest and join:

from itertools import zip_longest
abc = 'Hello World'
qwe = 'abc 123'
''.join(i+j for i, j in zip_longest(abc, qwe, fillvalue=''))

Output:

'Haeblcl o1 2W3orld'

edited May 23 '22 at 12:54

answered May 23 '22 at 12:20

Nin17

2,821
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Don't need to check for anything if you put fillvalue to ""! – Arwalk May 23 '22 at 12:52

Nikolaj Š. · Answer 4 · 2022-05-23T14:36:15.537

1

from itertools import chain, zip_longest

''.join(filter(None, chain.from_iterable(zip_longest(abc, qwe))))

or even

''.join(chain.from_iterable(zip_longest(abc, qwe, fillvalue='')))

(fillvalue suggested by Talha Tayyab in their answer)

edited May 23 '22 at 14:36

answered May 23 '22 at 12:28

Nikolaj Š.

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score 0 · Answer 5 · answered May 23 '22 at 12:22

0

Using zip and generator expression:

abc = 'Hello World'
qwe = 'abc 123'
min_len = min(len(abc), len(qwe))
print("".join(a+q for a,q in zip(abc, qwe)) + abc[min_len:] + qwe[min_len:])

(code for taking the ending of longer string from @LMD's answer)

answered May 23 '22 at 12:22

matszwecja

6,357
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Talha Tayyab · Answer 6 · 2022-05-23T15:32:52.610

0

from itertools import zip_longest
''.join(''.join(x) for x in zip_longest(abc,qwe,fillvalue =''))

edited May 23 '22 at 15:32

answered May 23 '22 at 12:33

Talha Tayyab

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there's no need to convert the zip to a list, could just be: ```''.join(''.join(x) for x in zip_longest(abc,qwe,fillvalue =''))``` – Nin17 May 23 '22 at 15:26

How to intersperse characters from two different strings alternatively to form a string

6 Answers6