Sanitize Field

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

Our exported records still carry a retired label, sometimes more than once inside the same text value. Return text with every occurrence of old swapped for new, and leave it untouched when old never appears.

Dirty input. Clean output.

Example 1

Input:

text = "status: legacy_ok, prev: legacy_ok", old = "legacy_ok", new = "ok"

Output:

"status: ok, prev: ok"

Example 2

Input:

text = "aaa", old = "a", new = "b"

Output:

"bbb"

Worked solution and explanation

Why this problem exists in real interviews

This is find-and-replace in a cleanup costume, and the logic is one call. What actually trips people is the contract: the grader calls str_replace(text=..., old=..., new=...) by keyword, so a function whose first parameter is named anything other than text raises TypeError before it replaces a single character. Match the signature, then make sure the replacement covers every occurrence, an empty new, an empty text, and a pattern that never shows up.

Break down the requirements

Step 1: Find and replace all occurrences

Every instance of old is swapped, not just the first, so a label repeated in one value is fully cleaned. An empty new deletes the label outright, and a text with no match comes back unchanged.

The solution

Built-in substring replacement
def str_replace(text, old, new):
    cleaned = text.replace(old, new)
    return cleaned

Common follow-up questions