How do I add the values in a list together? Python

Question

I'm currently learning Python and for my task it says to add the values of an array together. I tried:

no = ['1','2','3']
sum(no)

but had no luck in figuring out any way to find an answer. I'm also not supposed to use the sum function.

Here's an example of the question if you need more info:

Define a function sumStudentNo() that will add the individual digits of your student number (excluding any letters) using an array and display the answer. Eg If your student number is 's3456789' , your program should display 42 (ignore the 's' ).

Note you must NOT use the sum function.

Please help me.

Answer 1

If you are not allowed to use sum (as in sum(int(n) for n in no) ), then you have to 1) convert every list element using int and 2) sum them up.

s = 0
for n in no:
    try:
        s += int(n)
    except ValueError:
        pass

Answer 2

s = 0
no = "12p3s"
for i in no:
    if i.isdigit():
        s = s + int(i)
print s