Extract Digits

Write a function that pulls every run of digits out of a string.

extract_digits(s)

Return a comma-separated string of every consecutive run of digits found in s, in the order they appear. Return "" if there are none.

Examples

extract_digits("abc123def456")   // → "123,456"
extract_digits("a1b2c3")          // → "1,2,3"
extract_digits("no digits here")  // → ""

Walkthrough

Thinking it through

import re


def extract_digits(s):
    return ",".join(re.findall(r"\d+", s))

re.findall(r"\d+", s) scans the whole string and returns every match as a list — \d+ means "one or more consecutive digits", so it groups adjacent digits together as a single match rather than returning them one at a time. For "abc123def456", that's ["123", "456"] — two runs, not six individual digit matches.

",".join(...) then combines that list into the required comma-separated string. This is the same .join() you've used throughout the course — and it handles the empty case for free: joining an empty list produces "", which is exactly the required behavior when there are no digits at all.

main.py

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