Question

I would like to introduce look-and-say sequence at first. It goes like a = {1, 11, 21, 1211, 111221 ...

The system is it checks the previous digit and counts the numbers.

1 = one 1 (so = 11)
11 = two 1 (so = 21)
21 = one 2 one 1 (so = 1211)

As a rule of the sequence, no number can go beyond 3, so creating a translation table can fit in. But it is not semantic, I don’t like it.

What I want is, a script which evaluates the given value and return a look-and-say-alike string.

However, to go beyond out limits, I want it to even evaluate chars, so it can return 1A2b41.

I have been trying to make it work for hours, the logic went bad and I am having a brainfreeze at the moment.

Here is the script that actually doesn’t work(returns false results), but it can give you the idea, at least.

def seq(a):
    k,last,result,a = 1,'','',str(a)
    for i in range(len(a)):
        if last==a[i]:k+=1
        else:
            result = result+str(k)+a[i]
            k=1
        last = a[i]
    return result

Answer 1

I can see two issues with your code:

• The result is expanded by k and a[i] although the counter k does not count chars a[i] but chars last. Replace a[i] by last here (you may not want to add anything in the first round).

• After the loop you have to add the last value of the counter together with the last character again (this was not yet done), i.e. add another result = result+str(k)+last after the loop.

In total it looks like

def seq(a):
    a = str(a)
    k,last,result = 1,a[0],''
    for i in range(1,len(a)):
        if last==a[i]:k+=1
        else:
            result = result+str(k)+last
            k=1
        last = a[i]
    result = result+str(k)+last
    return result