The Alphabet Score

An easy Python interview practice problem on DataDriven. Write the Python and run it against test cases, with instant feedback.

Domain
Python
Difficulty
easy
Seniority
L3

Problem

Given a string, return the sum of alphabetic character values where a=1..z=26, case-insensitive. Non-alphabetic characters contribute 0.

Every letter has a secret numeric value - what's your total?

Example 1

Input:

s = "abc"

Output:

6

Example 2

Input:

s = "z"

Output:

26

Worked solution and explanation

Why this problem exists in real interviews

Character-to-value scoring tests whether you know the ord/chr ASCII trick or whether you'd build a 26-entry dict by hand. Interviewers grade this on how cleanly you state the alphabetic-only filter, how you handle case, and whether your final expression is a single sum() over a generator (Pythonic) or a manual accumulator (junior).

Break down the requirements

Step 1: Lowercase once, filter alphabetic

Lowercase the entire string up front so you only need one ord-anchor (ord('a')). Use str.isalpha() to skip non-letters; this also correctly handles digits, punctuation, and whitespace as zero contributions.

Step 2: Convert each letter with ord arithmetic

For a lowercase letter c, the value is ord(c) - ord('a') + 1. This maps 'a' to 1 and 'z' to 26 in one expression with no lookup table. Memorizing this idiom saves you from constructing a 26-item dict, which is the most common over-engineering.

Step 3: Sum in one expression

Wrap the conversion in a generator expression inside sum(). It runs in C, allocates no intermediate list, and reads as the spec sentence: 'sum of alphabetic character values.' Empty input returns 0 with no special case.

The solution

Lowercase, filter, ord-arithmetic, sum
def convert_string_mapping(s: str) -> int:
    s = s.lower()
    return sum(ord(c) - ord('a') + 1 for c in s if c.isalpha())

Common follow-up questions