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Problem with rearanging list with paired letters next to each others


On 2020-11-11, MRAB <python at mrabarnett.plus.com> wrote:
>> 
> Points to note in your first code:
>
> 1. Modifying a list while iterating over it is a bad idea.
>
> 2. You're modifying the list that you're passing in and also returning 
> it. That's a bad idea. Either modify it in place or modify and return a 
> copy.
>
> 3. The line:
>
>         m = (letter_list.index(x))
>
>     returns the position of the first occurrence of x.
>
> Points to note in your second code:
>
> 1. (See above)
>
> 2. (See above)
>
> 3. (See above)
>
> 4. 'i' goes from 0 to len(letter_list)-1, so i+1 goes from 1 to 
> len(letter_list), but the maximum index permitted by letter_list is 
> len(letter_list)-1, hence letter_list[i+1] will raise IndexError on the 
> last iteration.
>
> 5. 'i' goes from 0 to len(letter_list)-1, so i-1 goes from -1 to 
> len(letter_list)-2. letter_list[-1] returns the last (final) letter in 
> the list, and it's treated as a true.
>
> 6. This:
>
>         x != letter_list[i+1] and letter_list[i-1]
>
>     is checking whether:
>
>         x != letter_list[i+1]
>
>     is true and also whether:
>
>         letter_list[i-1]
>
>     is true.

I see now I overcomplicated it, what is a good idea then?