Input a string having some digits. Write a function to return the sum of digits present in this string.

Question

Accepted Answer

> [!TLDR]
> Walk the string once; ch.isdigit() picks out digit characters, int(ch) converts each to its numeric value, and a running total accumulates the sum.

**Idea.** The string mixes letters, digits and possibly symbols. A digit inside a string is a *character* ('7'), not a number, so two things are needed per character: a **test** — isdigit() — and a **conversion** — int(). Everything that is not a digit is skipped.

**Algorithm**

1. Set total = 0.
2. For every character ch in the string: if ch.isdigit(), do total += int(ch).
3. Return total.

```python
def sumDigits(st):
    """Return the sum of all digits present in string st."""
    total = 0
    for ch in st:
        if ch.isdigit():
            total += int(ch)   # '7' -> 7
    return total

# main program
s = input("Enter a string having digits: ")
print("Sum of digits in the string:", sumDigits(s))
```

**Trace** for st = "Class11Python3":

| ch | isdigit()? | total |
|----|------------|-------|
| C,l,a,s,s | no | 0 |
| 1 | yes | 1 |
| 1 | yes | 2 |
| P,y,t,h,o,n | no | 2 |
| 3 | yes | 5 |

**Sample runs**

```text
Enter a string having digits: Class11Python3
Sum of digits in the string: 5
```

```text
Enter a string having digits: a1b2c3d4 …

Q.Input a string having some digits. Write a function to return the sum of digits present in this string.

Concept understanding — Digit Sum Calculation

Digit Sum Calculation

The Intuition

The Precise Statement

Why It Works

Common Mistake …

Q.Input a string having some digits. Write a function to return the sum of digits present in this string.

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