Linear search checks items from the start until it finds the target or runs out. It works on an unsorted list. Worst case is n comparisons.

Goal

Return the index and the step count. Print a hit and a miss.

The loop

def linear_search(items, target):
    steps = 0
    for i, item in enumerate(items):
        steps += 1
        if item == target:
            return i, steps
    return -1, steps

cities = ["Nairobi", "Mombasa", "Kisumu", "Nakuru"]
print(linear_search(cities, "Kisumu"))
print(linear_search(cities, "Eldoret"))

Index 2 for Kisumu after 3 steps. -1 for a miss after 4 steps.

First match

def linear_search(items, target):
    steps = 0
    for i, item in enumerate(items):
        steps += 1
        if item == target:
            return i, steps
    return -1, steps

prices = [10.5, 22.0, 10.5, 31.0]
print(linear_search(prices, 10.5))

Duplicates: you get the first index.

From a file

Download cities.txt, Add files, then:

from pathlib import Path

def linear_search(items, target):
    steps = 0
    for i, item in enumerate(items):
        steps += 1
        if item == target:
            return i, steps
    return -1, steps

cities = Path("cities.txt").read_text(encoding="utf-8").splitlines()
print(cities)
print(linear_search(cities, "Nakuru"))

Pitfall

Python’s list.index raises ValueError on a miss. Returning -1 plus a step count makes the algorithm visible.