[Tutor] taking support of strings in solving numerical problems

[Alan Gauld]

On 24/10/2020 20:22, Manprit Singh wrote:

> Consider a problem a problem to find sum of series of the form :
> a + aa + aaa + aaa

> def sum_ser(x, lim):                   # definition
>     sum_no = 0
>     for i in range(lim):
>         sum_no = sum_no + int(str(x) * (i + 1))
>     return sum_no

> I have seen in various scenarios, where using strings in a numerical
> problem reduces the size of the program
> 
> Using strings to solve numerical problems in such a way is a valid use case
> ? should this practise be followed in production ?

It is valid in the few cases where it is helpful but usually
using math works better.

For example in your case the algorithm is simple

N2 = N1*10+x

Where N1 is the previous total and x is the number.
As a function:

def generate_nums(x,n):
   nums = [x]
   for i in range(1,n):
       nums.append(nums[-1]*10 +x)
   return nums

And the sum is just a case of applying sum():

>>> sum(generate_nums(9,4))
11106

And remember that string operations are quite slow compared
to math - in addition to the two way conversions you have
to create memory space, then expand that memory space.
All relatively slow operations.

Pure math will normally be faster.

-- 
Alan G
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