Can someone please explain this in detail for me?

Question

I just can't understand how this code works.

addition_str = '2+5+10+20'
s = 0
a = " "

for i in range(len(addition_str)):
if addition_str[i] <= "9" and addition_str[i] >= "0":
a += addition_str[i]

if addition_str[i] > "9" or addition_str[i] < "0" or i == len(addition_str) - 1:
s += int(a)
a = " "

print(s)

Answer 1

It first reading digits into 'a' until a non-digit encounters.
If on non-digit character, or at end, then 'a' is converted to int and added to 's'
a is reset to "" Empty.

So it's like
s = 2
s = s + 5 = 7
s = s + 10 = 17
s = s + 20 = 37

Hope it helps...

Answer 2

Visualize your code execution

(Python, Java, C, C++, JavaScript, Ruby)

https://pythontutor.com

Answer 3

I finally get it now. Thanks everyone for replying and explaining.