StopIteration Examples

Short, runnable programs that show python stopiteration in action. Read the explanation, press Run, then change the code and try your own ideas. New to the topic? Start with the Python StopIteration lesson.

1Skipping a header row with next()

Calling next() once on a file-like iterator reads the header, and the loop then continues with the remaining rows.

Skipping a header row with next()

import io

sales = io.StringIO("item,qty\nlamp,2\ndesk,1\nchair,4\n")
header = next(sales).strip().split(",")
print(header)

total = 0
for line in sales:
    total += int(line.split(",")[1])
print("units sold:", total)

Expected output['item', 'qty']
units sold: 7

2A generator that can be used only once

Generators are consumed by the first pass. Recreate the generator, or build a list, to use the values again.

A generator that can be used only once

def even_numbers(limit):
    for n in range(0, limit, 2):
        yield n

evens = even_numbers(8)
print(list(evens))
print(list(evens))
print(list(even_numbers(8)))

Expected output[0, 2, 4, 6]
[]
[0, 2, 4, 6]

3Pairing two lists with a shared iterator

zip() stops as soon as the shortest input is exhausted, and it handles the StopIteration internally.

Pairing two lists with a shared iterator

names = ["Asha", "Ben", "Chen"]
scores = iter([91, 78])

for name, score in zip(names, scores):
    print(name, score)

Expected outputAsha 91
Ben 78

4Returning a value from a generator

The value given to return inside a generator travels on the StopIteration exception as its value attribute.

Returning a value from a generator

def running_total(amounts):
    total = 0
    for amount in amounts:
        total += amount
        yield total
    return total

steps = running_total([5, 10, 20])
try:
    while True:
        print(next(steps))
except StopIteration as done:
    print("final:", done.value)

Expected output5
15
35
final: 35

5Cycling through a list with next()

itertools.cycle never runs out, so next() on it never raises StopIteration. Useful for round-robin assignments.

Cycling through a list with next()

from itertools import cycle

teams = cycle(["red", "blue"])
for player in ["Asha", "Ben", "Chen", "Dev"]:
    print(player, "->", next(teams))

Expected outputAsha -> red
Ben -> blue
Chen -> red
Dev -> blue

Practise next

Python StopIteration exercises → Back to the lesson

Python for Loops examples Python Exceptions: try, except, else and finally examples Python Generators, Iterators and yield examples Python Iterators examples