Value Replacement Recursion in Python

Question

Hi I have a question with regards to python programming for my assignment

The task is to replace the occurrence of a number in a given value in a recursive manner, and the final output must be in integer

i.e. digit_swap(521, 1, 3) --> 523 where 1 is swapped out for 3

Below is my code and it works well for s = 0 - 9 if the final answer is outputted as string

def digit_swap(n, d, s):
    result = ""
    if len(str(n)) == 1:
        if str(n) == str(d):
            return str(s)
        else:
            return str(n)
    elif str(n)[0] == str(d):
        result = result + str(s) + str(digit_swap(str(n)[1:], d, s))
        return result
    else:
        result = result + str(n)[0] + str(digit_swap(str(n)[1:], d, s))
        return result

However, I have trouble making the final output as Integer The code breaks down when s = 0 i.e. digit_swap(65132, 1, 0) --> 6532 instead of 65032

Is there any fix to my code?

def digit_swap(n, d, s):
    result = ""
    if len(str(n)) == 1:
        if str(n) == str(d):
            return str(s)
        else:
            return str(n)
    elif str(n)[0] == str(d):
        result = result + str(s) + str(digit_swap(str(n)[1:], d, s))
        return int(result) # Changes
    else:
        result = result + str(n)[0] + str(digit_swap(str(n)[1:], d, s))
        return int(result) # Changes

This is very unclear to me, if I understand your question correctly, the second example should be 6500 and not 651. — IMCoins
– IMCoins, Commented Feb 27, 2019 at 8:33
@IMCoins - That's where the code breaks down, the unwanted behavior produced by the given code. — TigerhawkT3
– TigerhawkT3, Commented Feb 27, 2019 at 8:35
@IMCoins I apologize and I have edited the phrasing more clearly, if I used the second code for digit_swap(65132, 1, 0) , I will get 6532 instead of 65032 as the recursive method will make "032" an integer, resulting in 32 I'm not too sure if there are other ways to convert from string to integer for the final output for a recursive method — Tan Guan Quan
– Tan Guan Quan, Commented Feb 27, 2019 at 8:41

Habibutsu · Accepted Answer · 2019-02-27 09:12:50Z

1

Conversion to string is unnecessary, this can be implemented much easier

def digit_swap(n, d, s):
    if n == 0:
        return 0
    lower_n  = (s if (n % 10) == d else (n % 10))
    higher_n = digit_swap(n // 10, d, s) * 10
return higher_n + lower_n

assert digit_swap(521, 1, 3) == 523
assert digit_swap(65132, 1, 0) == 65032

answered Feb 27, 2019 at 9:12

Habibutsu

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Comments

PuNiT · Accepted Answer · 2019-02-27 08:44:51Z

0

do not return int from method, instead convert it to int from where you are calling method. Problem lies where your code trying to convert string to int return int(result). So if result is 03 then function will return int('03') i.e 3. call your method like this print int(digit_swap(65132, 1, 0)) so you will get integer at the end.

answered Feb 27, 2019 at 8:44

PuNiT

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Simon Schrodi · Accepted Answer · 2019-02-27 08:54:23Z

0

For example int(00) is casted to 0. Therefore a zero is discarded. I suggest not to cast, instead leave it as a string. If you have to give back an int, you should not cast until you return the number. However, you still discard 0s at the beginning. So all in all, I would suggest just return strings instead of ints:

return str(result) # instead of return int(result)

And call it:

int(digit_swap(n,d,s))

edited Feb 27, 2019 at 8:54

answered Feb 27, 2019 at 8:41

Simon Schrodi

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