Extract Domain

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 URL string containing '://', return the substring between '://' and the next '/' (or end of string if no trailing slash).

The domain is buried in the string.

Example 1

Input:

url = "https://api.example.com/v2/data"

Output:

"api.example.com"

Example 2

Input:

url = "http://localhost:8080/health"

Output:

"localhost:8080"

Worked solution and explanation

Why this problem exists in real interviews

Extracting a domain from a URL tests string splitting and indexing, a pattern that appears constantly in log parsing and ETL pipelines. It checks whether you can find substrings between delimiters efficiently.

Break down the requirements

Step 1: Find the position after ://

Split on '://' and take the part after it. This isolates everything after the protocol.

Step 2: Take everything before the next /

Split the remainder on '/' and take the first segment. This gives the domain.

The solution

Delimiter-based extraction with split

def extract_domain(url):
    after_protocol = url.split('://')[1]
    domain = after_protocol.split('/')[0]
    return domain

Common follow-up questions

What if the URL has a port number like 'https://example.com:8080/path'? (Tests splitting on ':' after the protocol to separate domain and port.)
How would you extract the subdomain separately? (Tests splitting the domain on '.' and taking all but the last two segments.)
What if the URL is malformed and has no ://? (Tests error handling: return an empty string or raise a ValueError.)